From d0bae0b218d54aedb439381e5e4480e862f42f8b Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Sat, 8 Aug 2020 12:15:09 +0100
Subject: [PATCH] Darwin: Adjust the PCH area to allow for 16384byte page size.

Newer versions of Darwin report pagesize 20 which means that we
need to adjust the aligment of the PCH area.

gcc/ChangeLog:

	* config/host-darwin.c: Align pch_address_space to 16384.

(cherry picked from commit 590febb5f6624f78b36402a7c9a9c318978f1efa)
---
 gcc/config/host-darwin.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/gcc/config/host-darwin.c b/gcc/config/host-darwin.c
index 0face6c450f3..c862935dcf31 100644
--- a/gcc/config/host-darwin.c
+++ b/gcc/config/host-darwin.c
@@ -24,7 +24,10 @@
 #include "config/host-darwin.h"
 
 /* Yes, this is really supposed to work.  */
-static char pch_address_space[1024*1024*1024] __attribute__((aligned (4096)));
+/* This allows for a pagesize of 16384, which we have on Darwin20, but should
+   continue to work OK for pagesize 4096 which we have on earlier versions.
+   The size is 1 (binary) Gb.  */
+static char pch_address_space[65536*16384] __attribute__((aligned (16384)));
 
 /* Return the address of the PCH address space, if the PCH will fit in it.  */
 
From 24957662c670c92b2260debb029893c6e91b2979 Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Fri, 31 Jul 2020 21:05:28 +0100
Subject: [PATCH] Darwin: Darwin 20 is to be macOS 11 (Big Sur).
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

As per Nigel Tufnel's assertion "... this one goes to 11".

The various parts of the code that deal with mapping Darwin versions
to macOS (X) versions need updating to deal with  a major version of
11.

So now we have, for example:

Darwin  4 => macOS (X) 10.0
…
Darwin 14 => macOS (X) 10.10
...
Darwin 19 => macOS (X) 10.15

Darwin 20 => macOS  11.0

Because of the historical duplication of the "10" in macOSX 10.xx and
the number of tools that expect this, it is likely that system tools will
allow macos11.0 and/or macosx11.0 (despite that the latter makes little
sense).

Update the link test to cover Catalina (Darwin19/10.15) and
Big Sur (Darwin20/11.0).

gcc/ChangeLog:

	* config/darwin-c.c: Allow for Darwin20 to correspond to macOS 11.
	* config/darwin-driver.c: Likewise.

gcc/testsuite/ChangeLog:

	* gcc.dg/darwin-minversion-link.c: Allow for Darwin19 (macOS 10.15)
	and Darwin20 (macOS 11.0).

(cherry picked from commit 556ab5125912fa2233986eb19d6cd995cf7de1d2)
---
 gcc/config/darwin-c.c                         |  4 ++--
 gcc/config/darwin-driver.c                    | 21 ++++++++++++-------
 gcc/testsuite/gcc.dg/darwin-minversion-link.c |  5 +++--
 3 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/gcc/config/darwin-c.c b/gcc/config/darwin-c.c
index e3b999e166b2..9034f49908e0 100644
--- a/gcc/config/darwin-c.c
+++ b/gcc/config/darwin-c.c
@@ -692,10 +692,10 @@ macosx_version_as_macro (void)
   if (!version_array)
     goto fail;
 
-  if (version_array[MAJOR] != 10)
+  if (version_array[MAJOR] < 10 || version_array[MAJOR] > 11)
     goto fail;
 
-  if (version_array[MINOR] < 10)
+  if (version_array[MAJOR] == 10 && version_array[MINOR] < 10)
     version_macro = version_as_legacy_macro (version_array);
   else
     version_macro = version_as_modern_macro (version_array);
diff --git a/gcc/config/darwin-driver.c b/gcc/config/darwin-driver.c
index 6cf85d04b699..2df433ad716c 100644
--- a/gcc/config/darwin-driver.c
+++ b/gcc/config/darwin-driver.c
@@ -65,7 +65,7 @@ validate_macosx_version_min (const char *version_str)
   major = strtoul (version_str, &end, 10);
   version_str = end + ((*end == '.') ? 1 : 0);
 
-  if (major != 10) /* So far .. all MacOS 10 ... */
+  if (major < 10 || major > 11 ) /* MacOS 10 and 11 are known. */
     return NULL;
 
   /* Version string components must be present and numeric.  */
@@ -104,7 +104,7 @@ validate_macosx_version_min (const char *version_str)
   if (need_rewrite)
     {
       char *new_version;
-      asprintf (&new_version, "10.%lu.%lu", minor, tiny);
+      asprintf (&new_version, "%2lu.%lu.%lu", major, minor, tiny);
       return new_version;
     }
 
@@ -115,6 +115,12 @@ validate_macosx_version_min (const char *version_str)
 #include <sys/sysctl.h>
 #include "xregex.h"
 
+/* Determine the version of the running OS.
+   We only look at the first two components (ignoring the patch one) and
+   report NN.MM.0 where NN is currently either 10 or 11 and MM is the OS
+   minor release number.
+   If we can't parse what the kernel gives us, warn the user, and do nothing.  */
+
 static char *
 darwin_find_version_from_kernel (void)
 {
@@ -125,8 +131,6 @@ darwin_find_version_from_kernel (void)
   char * version_p;
   char * new_flag;
 
-  /* Determine the version of the running OS.  If we can't, warn user,
-     and do nothing.  */
   if (sysctl (osversion_name, ARRAY_SIZE (osversion_name), osversion,
 	      &osversion_len, NULL, 0) == -1)
     {
@@ -144,10 +148,11 @@ darwin_find_version_from_kernel (void)
     major_vers = major_vers * 10 + (*version_p++ - '0');
   if (*version_p++ != '.')
     goto parse_failed;
-  
-  /* The major kernel version number is 4 plus the second OS version
-     component.  */
-  if (major_vers - 4 <= 4)
+
+  /* Darwin20 sees a transition to macOS 11.  */
+  if (major_vers >= 20)
+    asprintf (&new_flag, "11.%02d.00", major_vers - 20);
+  else if (major_vers - 4 <= 4)
     /* On 10.4 and earlier, the old linker is used which does not
        support three-component system versions.
        FIXME: we should not assume this - a newer linker could be used.  */
diff --git a/gcc/testsuite/gcc.dg/darwin-minversion-link.c b/gcc/testsuite/gcc.dg/darwin-minversion-link.c
index 0a80048ba354..765fb799a918 100644
--- a/gcc/testsuite/gcc.dg/darwin-minversion-link.c
+++ b/gcc/testsuite/gcc.dg/darwin-minversion-link.c
@@ -13,8 +13,9 @@
 /* { dg-additional-options "-mmacosx-version-min=010.011.06 -DCHECK=101106" { target *-*-darwin15* } } */
 /* { dg-additional-options "-mmacosx-version-min=010.012.06 -DCHECK=101206" { target *-*-darwin16* } } */
 /* { dg-additional-options "-mmacosx-version-min=010.013.06 -DCHECK=101306" { target *-*-darwin17* } } */
-/* This next test covers 10.18 and (currently unreleased) 10.19 for now. */  
-/* { dg-additional-options "-mmacosx-version-min=010.014.05 -DCHECK=101405" { target *-*-darwin1[89]* } } */
+/* { dg-additional-options "-mmacosx-version-min=010.014.05 -DCHECK=101405" { target *-*-darwin18* } } */
+/* { dg-additional-options "-mmacosx-version-min=010.015.06 -DCHECK=101506" { target *-*-darwin19* } } */
+/* { dg-additional-options "-mmacosx-version-min=011.000.00 -DCHECK=110000" { target *-*-darwin20 } } */
 
 int
 main ()
From f5ee16a0d8e31d1754e760e984623194de8e56d7 Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Sat, 19 Dec 2020 13:05:34 +0000
Subject: [PATCH] Darwin : Update the kernel version to macOS version mapping.

With the change to macOS 11 and Darwin20, the algorithm for mapping
kernel version to macOS version has changed.

We now have darwin 20.X.Y => macOS 11.(X > 0 ? X - 1 : 0).??.
It currently unclear if the Y will be mapped to macOS patch version
and, if so, whether it will be one-based or 0-based.
Likewise, it's unknown if Darwin 21 will map to macOS 12, so these
entries are unchanged for the present.

gcc/ChangeLog:

	* config/darwin-driver.c (darwin_find_version_from_kernel):
	Compute the minor OS version from the minor kernel version.
---
 gcc/config/darwin-driver.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/gcc/config/darwin-driver.c b/gcc/config/darwin-driver.c
index 2df433ad716c..0fff7b70f35e 100644
--- a/gcc/config/darwin-driver.c
+++ b/gcc/config/darwin-driver.c
@@ -149,9 +149,22 @@ darwin_find_version_from_kernel (void)
   if (*version_p++ != '.')
     goto parse_failed;
 
-  /* Darwin20 sees a transition to macOS 11.  */
+  /* Darwin20 sees a transition to macOS 11.  In this, it seems that the
+     mapping to macOS minor version is now shifted to the kernel minor
+     version - 1 (at least for the initial releases).  At this stage, we
+     don't know what macOS version will correspond to Darwin21.  */
   if (major_vers >= 20)
-    asprintf (&new_flag, "11.%02d.00", major_vers - 20);
+    {
+      int minor_vers = *version_p++ - '0';
+      if (ISDIGIT (*version_p))
+	minor_vers = minor_vers * 10 + (*version_p++ - '0');
+      if (*version_p++ != '.')
+	goto parse_failed;
+      if (minor_vers > 0)
+	minor_vers -= 1; /* Kernel 20.3 => macOS 11.2.  */
+      /* It's not yet clear whether patch level will be considered.  */
+      asprintf (&new_flag, "11.%02d.00", minor_vers);
+    }
   else if (major_vers - 4 <= 4)
     /* On 10.4 and earlier, the old linker is used which does not
        support three-component system versions.
From 82abd13fb66e088bb1bc858f0209c201cde79580 Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Wed, 23 Dec 2020 17:16:08 +0000
Subject: [PATCH] Darwin : Adjust handling of MACOSX_DEPLOYMENT_TARGET for
 macOS 11.

The shift to macOS version 11 also means that '11' without any
following '.x' is accepted as a valid version number.  This adjusts
the validation code to accept this and map it to 11.0.0 which
matches what the clang toolchain appears to do.

gcc/ChangeLog:

	* config/darwin-driver.c (validate_macosx_version_min): Allow
	MACOSX_DEPLOYMENT_TARGET=11.
	(darwin_default_min_version): Adjust warning spelling to avoid
	an apostrophe.
---
 gcc/config/darwin-driver.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/gcc/config/darwin-driver.c b/gcc/config/darwin-driver.c
index 0fff7b70f35e..f00d5a02d1d0 100644
--- a/gcc/config/darwin-driver.c
+++ b/gcc/config/darwin-driver.c
@@ -43,13 +43,13 @@ static const char *
 validate_macosx_version_min (const char *version_str)
 {
   size_t version_len;
-  unsigned long major, minor, tiny = 0;
+  unsigned long major, minor = 0, tiny = 0;
   char *end;
   const char *old_version = version_str;
   bool need_rewrite = false;
 
   version_len = strlen (version_str);
-  if (version_len < 4) /* The minimum would be 10.x  */
+  if (version_len < 2) /* The minimum would be 11  */
     return NULL;
 
   /* Version string must consist of digits and periods only.  */
@@ -63,18 +63,27 @@ validate_macosx_version_min (const char *version_str)
     need_rewrite = true;
 
   major = strtoul (version_str, &end, 10);
-  version_str = end + ((*end == '.') ? 1 : 0);
 
   if (major < 10 || major > 11 ) /* MacOS 10 and 11 are known. */
     return NULL;
 
-  /* Version string components must be present and numeric.  */
-  if (!ISDIGIT (version_str[0]))
+  /* Skip a separating period, if there's one.  */
+  version_str = end + ((*end == '.') ? 1 : 0);
+
+  if (major == 11 && *end != '\0' && !ISDIGIT (version_str[0]))
+     /* For MacOS 11, we allow just the major number, but if the minor is
+	there it must be numeric.  */
+    return NULL;
+  else if (major == 11 && *end == '\0')
+    /* We will rewrite 11 =>  11.0.0.  */
+    need_rewrite = true;
+  else if (major == 10 && (*end == '\0' || !ISDIGIT (version_str[0])))
+    /* Otherwise, minor version components must be present and numeric.  */
     return NULL;
 
   /* If we have one or more leading zeros on a component, then rewrite the
      version string.  */
-  if (version_str[0] == '0' && version_str[1] != '\0'
+  if (*end != '\0' && version_str[0] == '0' && version_str[1] != '\0'
       && version_str[1] != '.')
     need_rewrite = true;
 
@@ -220,7 +229,7 @@ darwin_default_min_version (void)
       const char *checked = validate_macosx_version_min (new_flag);
       if (checked == NULL)
 	{
-	  warning (0, "couldn%'t understand version %s", new_flag);
+	  warning (0, "could not understand version %s", new_flag);
 	  return NULL;
 	}
       new_flag = xstrndup (checked, strlen (checked));
From 7b19b6b15368c6157d2261015fbb94c8c07c104a Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Wed, 18 Nov 2020 13:15:47 +0000
Subject: [PATCH] Darwin, libsanitizer : Support libsanitizer for
 x86_64-darwin20.

The sanitizer is supported for at least x86_64 and Darwin20.

libsanitizer/ChangeLog:

	* configure.tgt: Allow x86_64 Darwin2x.

(cherry picked from commit 93f1186f7d3419c7af692295bd509d7bfaf170a1)
---
 libsanitizer/configure.tgt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libsanitizer/configure.tgt b/libsanitizer/configure.tgt
index 5d46990eba4d..79084e58afbc 100644
--- a/libsanitizer/configure.tgt
+++ b/libsanitizer/configure.tgt
@@ -60,7 +60,7 @@ case "${target}" in
 		TSAN_TARGET_DEPENDENT_OBJECTS=tsan_rtl_aarch64.lo
 	fi
 	;;
-  x86_64-*-darwin1[2-9]* | i?86-*-darwin1[2-9]*)
+  x86_64-*-darwin2* | x86_64-*-darwin1[2-9]* | i?86-*-darwin1[2-9]*)
 	TSAN_SUPPORTED=no
 	;;
   x86_64-*-solaris2.11* | i?86-*-solaris2.11*)
From c85bc938ccf75ea45c00e430f715544ff396e5b5 Mon Sep 17 00:00:00 2001
From: Iain Sandoe <iain@sandoe.co.uk>
Date: Wed, 18 Nov 2020 10:06:03 +0000
Subject: [PATCH] Darwin : Update libtool and dependencies for Darwin20
 [PR97865]

The change in major version (and the increment from Darwin19 to 20)
caused libtool tests to fail which resulted in incorrect build settings
for shared libraries.

We take this opportunity to sort out the shared undefined symbols state
rather than propagating the current unsound behaviour into a new rev.

This change means that we default to the case that missing symbols are
considered an error, and if one wants to allow this intentionally, the
confiuration for that case should be set appropriately.

Three existing cases need undefined dynamic lookup:
 libitm, where there is already a configuration mechanism to add the
         flags.
 libcc1, where we add simple configuration to add the flags for Darwin.
 libsanitizer, where we can add to the existing extra flags.

	Backported from 1352bc88a0525743c952197fb2db6e4f8c091cde and 5dc998933e7aa737f4a45a8a2885d42d5288d51a

libcc1/ChangeLog:

	PR target/97865
	* Makefile.am: Add dynamic_lookup to LD flags for Darwin.
	* configure.ac: Test for Darwin host and set a flag.
	* Makefile.in: Regenerate.
	* configure: Regenerate.

libitm/ChangeLog:

	PR target/97865
	* configure.tgt: Add dynamic_lookup to XLDFLAGS for Darwin.
	* configure: Regenerate.

libsanitizer/ChangeLog:

	PR target/97865
	* configure.tgt: Add dynamic_lookup to EXTRA_CXXFLAGS for
	Darwin.
	* configure: Regenerate.

ChangeLog:

	PR target/97865
	* libtool.m4: Update handling of Darwin platform link flags
	for Darwin20.

gcc/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libatomic/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libbacktrace/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libffi/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libgfortran/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libgomp/ChangeLog:

	PR target/97865
	* configure: Regenerate.
	* Makefile.in: Update copyright years.

libhsail-rt/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libobjc/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libphobos/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libquadmath/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libssp/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libstdc++-v3/ChangeLog:

	PR target/97865
	* configure: Regenerate.

libvtv/ChangeLog:

	PR target/97865
	* configure: Regenerate.

zlib/ChangeLog:

	PR target/97865
	* configure: Regenerate.

Co-Authored-By: Jakub Jelinek  <jakub@redhat.com>
---
 gcc/configure              | 34 ++++++++++++------------
 libatomic/configure        | 34 ++++++++++++------------
 libbacktrace/configure     | 34 ++++++++++++------------
 libcc1/Makefile.am         |  3 +++
 libcc1/Makefile.in         |  3 ++-
 libcc1/configure           | 53 ++++++++++++++++++++++++++------------
 libcc1/configure.ac        |  6 +++++
 libffi/configure           | 34 ++++++++++++------------
 libgfortran/configure      | 34 ++++++++++++------------
 libgomp/Makefile.in        |  2 +-
 libgomp/configure          | 34 ++++++++++++------------
 libhsail-rt/configure      | 34 ++++++++++++------------
 libitm/configure           | 34 ++++++++++++------------
 libitm/configure.tgt       |  9 ++++++-
 libobjc/configure          | 34 ++++++++++++------------
 libphobos/configure        | 34 ++++++++++++------------
 libquadmath/configure      | 34 ++++++++++++------------
 libsanitizer/configure     | 34 ++++++++++++------------
 libsanitizer/configure.tgt |  1 +
 libssp/configure           | 34 ++++++++++++------------
 libstdc++-v3/configure     | 48 +++++++++++++++++-----------------
 libtool.m4                 | 32 ++++++++++++-----------
 libvtv/configure           | 34 ++++++++++++------------
 zlib/configure             | 38 ++++++++++++++-------------
 24 files changed, 372 insertions(+), 299 deletions(-)

diff --git a/gcc/configure b/gcc/configure
index 4fa977217a75..8fe9c91fd7c2 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -15490,23 +15490,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libatomic/configure b/libatomic/configure
index 3e2f2ff4f202..6e706e90636b 100755
--- a/libatomic/configure
+++ b/libatomic/configure
@@ -7589,23 +7589,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libbacktrace/configure b/libbacktrace/configure
index 28b9593342a9..6a0dd7602fe1 100755
--- a/libbacktrace/configure
+++ b/libbacktrace/configure
@@ -7968,23 +7968,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libcc1/Makefile.am b/libcc1/Makefile.am
index c005b0dad4a8..fe7b64cbc6fe 100644
--- a/libcc1/Makefile.am
+++ b/libcc1/Makefile.am
@@ -25,6 +25,9 @@ CPPFLAGS_FOR_C_FAMILY = -I $(srcdir)/../gcc/c-family \
 CPPFLAGS_FOR_C = $(CPPFLAGS_FOR_C_FAMILY) -I $(srcdir)/../gcc/c
 CPPFLAGS_FOR_CXX = $(CPPFLAGS_FOR_C_FAMILY) -I $(srcdir)/../gcc/cp
 AM_CXXFLAGS = $(WARN_FLAGS) $(WERROR) $(visibility)
+if DARWIN_DYNAMIC_LOOKUP
+AM_CXXFLAGS += -Wl,-undefined,dynamic_lookup
+endif
 override CXXFLAGS := $(filter-out -fsanitize=address,$(CXXFLAGS))
 override LDFLAGS := $(filter-out -fsanitize=address,$(LDFLAGS))
 # Can be simplified when libiberty becomes a normal convenience library.
diff --git a/libcc1/Makefile.in b/libcc1/Makefile.in
index 7104b649026b..2def836cb06a 100644
--- a/libcc1/Makefile.in
+++ b/libcc1/Makefile.in
@@ -89,6 +89,7 @@ POST_UNINSTALL = :
 build_triplet = @build@
 host_triplet = @host@
 target_triplet = @target@
+@DARWIN_DYNAMIC_LOOKUP_TRUE@am__append_1 = -Wl,-undefined,dynamic_lookup
 subdir = .
 ACLOCAL_M4 = $(top_srcdir)/aclocal.m4
 am__aclocal_m4_deps = $(top_srcdir)/../config/acx.m4 \
@@ -382,7 +383,7 @@ CPPFLAGS_FOR_C_FAMILY = -I $(srcdir)/../gcc/c-family \
 
 CPPFLAGS_FOR_C = $(CPPFLAGS_FOR_C_FAMILY) -I $(srcdir)/../gcc/c
 CPPFLAGS_FOR_CXX = $(CPPFLAGS_FOR_C_FAMILY) -I $(srcdir)/../gcc/cp
-AM_CXXFLAGS = $(WARN_FLAGS) $(WERROR) $(visibility)
+AM_CXXFLAGS = $(WARN_FLAGS) $(WERROR) $(visibility) $(am__append_1)
 # Can be simplified when libiberty becomes a normal convenience library.
 libiberty_normal = ../libiberty/libiberty.a
 libiberty_noasan = ../libiberty/noasan/libiberty.a
diff --git a/libcc1/configure b/libcc1/configure
index 64fdc4451630..f1c64d86b525 100755
--- a/libcc1/configure
+++ b/libcc1/configure
@@ -635,6 +635,8 @@ LTLIBOBJS
 LIBOBJS
 ENABLE_PLUGIN_FALSE
 ENABLE_PLUGIN_TRUE
+DARWIN_DYNAMIC_LOOKUP_FALSE
+DARWIN_DYNAMIC_LOOKUP_TRUE
 libsuffix
 GMPINC
 WERROR
@@ -7250,23 +7252,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
@@ -14781,6 +14785,19 @@ fi
 $as_echo "$libcc1_cv_lib_sockets" >&6; }
 LIBS="$LIBS $libcc1_cv_lib_sockets"
 
+case "$host" in
+  *-*-darwin*) darwin_dynamic_lookup=yes ;;
+  *) darwin_dynamic_lookup=no ;;
+esac
+ if test $darwin_dynamic_lookup = yes; then
+  DARWIN_DYNAMIC_LOOKUP_TRUE=
+  DARWIN_DYNAMIC_LOOKUP_FALSE='#'
+else
+  DARWIN_DYNAMIC_LOOKUP_TRUE='#'
+  DARWIN_DYNAMIC_LOOKUP_FALSE=
+fi
+
+
 # If any of these functions are missing, simply don't bother building
 # this plugin.
 # Check for plugin support
@@ -15149,6 +15166,10 @@ if test -z "${am__fastdepCXX_TRUE}" && test -z "${am__fastdepCXX_FALSE}"; then
   as_fn_error $? "conditional \"am__fastdepCXX\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
 fi
+if test -z "${DARWIN_DYNAMIC_LOOKUP_TRUE}" && test -z "${DARWIN_DYNAMIC_LOOKUP_FALSE}"; then
+  as_fn_error $? "conditional \"DARWIN_DYNAMIC_LOOKUP\" was never defined.
+Usually this means the macro was only invoked conditionally." "$LINENO" 5
+fi
 if test -z "${ENABLE_PLUGIN_TRUE}" && test -z "${ENABLE_PLUGIN_FALSE}"; then
   as_fn_error $? "conditional \"ENABLE_PLUGIN\" was never defined.
 Usually this means the macro was only invoked conditionally." "$LINENO" 5
diff --git a/libcc1/configure.ac b/libcc1/configure.ac
index 7f20f0b6f680..1a46989e3b6f 100644
--- a/libcc1/configure.ac
+++ b/libcc1/configure.ac
@@ -101,6 +101,12 @@ AC_CACHE_CHECK([for socket libraries], libcc1_cv_lib_sockets,
 ])
 LIBS="$LIBS $libcc1_cv_lib_sockets"
 
+case "$host" in
+  *-*-darwin*) darwin_dynamic_lookup=yes ;;
+  *) darwin_dynamic_lookup=no ;;
+esac
+AM_CONDITIONAL(DARWIN_DYNAMIC_LOOKUP, test $darwin_dynamic_lookup = yes)
+
 # If any of these functions are missing, simply don't bother building
 # this plugin.
 GCC_ENABLE_PLUGINS
diff --git a/libffi/configure b/libffi/configure
index f0051505d104..b32e109f0302 100755
--- a/libffi/configure
+++ b/libffi/configure
@@ -7762,23 +7762,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libgfortran/configure b/libgfortran/configure
index b4cf854ddb39..1b4a8b106096 100755
--- a/libgfortran/configure
+++ b/libgfortran/configure
@@ -9163,23 +9163,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libgomp/Makefile.in b/libgomp/Makefile.in
index 7c426caeb682..ae5d9d547053 100644
--- a/libgomp/Makefile.in
+++ b/libgomp/Makefile.in
@@ -16,7 +16,7 @@
 
 # Plugins for offload execution, Makefile.am fragment.
 #
-# Copyright (C) 2014-2019 Free Software Foundation, Inc.
+# Copyright (C) 2014-2020 Free Software Foundation, Inc.
 #
 # Contributed by Mentor Embedded.
 #
diff --git a/libgomp/configure b/libgomp/configure
index d8d98f182d4c..69f57e315218 100755
--- a/libgomp/configure
+++ b/libgomp/configure
@@ -7634,23 +7634,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libhsail-rt/configure b/libhsail-rt/configure
index 49d529c8f5fe..33e61484333f 100755
--- a/libhsail-rt/configure
+++ b/libhsail-rt/configure
@@ -7442,23 +7442,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libitm/configure b/libitm/configure
index 97db1bc8845c..ea31a1d5cdda 100755
--- a/libitm/configure
+++ b/libitm/configure
@@ -8265,23 +8265,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libitm/configure.tgt b/libitm/configure.tgt
index 04109160e91c..d1beb5c9ec85 100644
--- a/libitm/configure.tgt
+++ b/libitm/configure.tgt
@@ -43,6 +43,7 @@ if test "$gcc_cv_have_tls" = yes ; then
     *-*-linux*)
 	XCFLAGS="${XCFLAGS} -ftls-model=initial-exec"
 	;;
+
   esac
 fi
 
@@ -144,10 +145,16 @@ case "${target}" in
   *-*-gnu* | *-*-k*bsd*-gnu \
   | *-*-netbsd* | *-*-freebsd* | *-*-openbsd* \
   | *-*-solaris2* | *-*-sysv4* | *-*-hpux11* \
-  | *-*-darwin* | *-*-aix* | *-*-dragonfly*)
+  | *-*-aix* | *-*-dragonfly*)
 	# POSIX system.  The OS is supported.
 	;;
 
+  *-*-darwin*)
+	# The OS is supported, but we need dynamic lookup to support undefined
+	# weak symbols at link-time.
+	XLDFLAGS="${XLDFLAGS} -Wl,-undefined,dynamic_lookup"
+	;;
+
   *)	# Non-POSIX, or embedded system
 	UNSUPPORTED=1
 	;;
diff --git a/libobjc/configure b/libobjc/configure
index 2f8924e5042f..32c389f13859 100755
--- a/libobjc/configure
+++ b/libobjc/configure
@@ -6952,23 +6952,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libphobos/configure b/libphobos/configure
index e461c7442b29..29595b938f62 100755
--- a/libphobos/configure
+++ b/libphobos/configure
@@ -8117,23 +8117,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libquadmath/configure b/libquadmath/configure
index 7b45eb7e805f..b5b212c06392 100755
--- a/libquadmath/configure
+++ b/libquadmath/configure
@@ -7256,23 +7256,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libsanitizer/configure b/libsanitizer/configure
index 0c56bdf2d7d4..ed0c15e37fc7 100755
--- a/libsanitizer/configure
+++ b/libsanitizer/configure
@@ -8831,23 +8831,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libsanitizer/configure.tgt b/libsanitizer/configure.tgt
index 79084e58afbc..fa30065b5954 100644
--- a/libsanitizer/configure.tgt
+++ b/libsanitizer/configure.tgt
@@ -62,6 +62,7 @@ case "${target}" in
 	;;
   x86_64-*-darwin2* | x86_64-*-darwin1[2-9]* | i?86-*-darwin1[2-9]*)
 	TSAN_SUPPORTED=no
+	EXTRA_CXXFLAGS+="-Wl,-undefined,dynamic_lookup"
 	;;
   x86_64-*-solaris2.11* | i?86-*-solaris2.11*)
 	;;
diff --git a/libssp/configure b/libssp/configure
index dd3b41da0f62..db527f475195 100755
--- a/libssp/configure
+++ b/libssp/configure
@@ -7438,23 +7438,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index b9c9b844c278..e7a069c567eb 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -8373,23 +8373,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/libtool.m4 b/libtool.m4
index e194e899fcfb..00206549f540 100644
--- a/libtool.m4
+++ b/libtool.m4
@@ -994,23 +994,25 @@ _LT_EOF
         rm -f conftest.err libconftest.a conftest conftest.c
         rm -rf conftest.dSYM
     ])
-    case $host_os in
-    rhapsody* | darwin1.[[012]])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[[012]])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[[91]]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[[89]]*|UNSET,*-darwin[[12]][[0123456789]]*)
+	  ;;
 	10.[[012]][[,.]]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
@@ -1033,7 +1035,7 @@ _LT_EOF
 
 # _LT_DARWIN_LINKER_FEATURES
 # --------------------------
-# Checks for linker and compiler features on darwin
+# Checks for linker and compiler features on Darwin / macOS / iOS
 m4_defun([_LT_DARWIN_LINKER_FEATURES],
 [
   m4_require([_LT_REQUIRED_DARWIN_CHECKS])
diff --git a/libvtv/configure b/libvtv/configure
index fc969525da01..4de60cf5e501 100755
--- a/libvtv/configure
+++ b/libvtv/configure
@@ -8732,23 +8732,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then
diff --git a/zlib/configure b/zlib/configure
index 484a4938f4a8..46a35918ddbd 100755
--- a/zlib/configure
+++ b/zlib/configure
@@ -3400,11 +3400,11 @@ done
 
 cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
+#include <stdio.h>
 int
 main ()
 {
-
+printf ("hello world\n");
   ;
   return 0;
 }
@@ -6827,23 +6827,25 @@ _LT_EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $lt_cv_ld_force_load" >&5
 $as_echo "$lt_cv_ld_force_load" >&6; }
-    case $host_os in
-    rhapsody* | darwin1.[012])
+    # Allow for Darwin 4-7 (macOS 10.0-10.3) although these are not expect to
+    # build without first building modern cctools / linker.
+    case $host_cpu-$host_os in
+    *-rhapsody* | *-darwin1.[012])
       _lt_dar_allow_undefined='${wl}-undefined ${wl}suppress' ;;
-    darwin1.*)
+    *-darwin1.*)
       _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-    darwin*) # darwin 5.x on
-      # if running on 10.5 or later, the deployment target defaults
-      # to the OS version, if on x86, and 10.4, the deployment
-      # target defaults to 10.4. Don't you love it?
-      case ${MACOSX_DEPLOYMENT_TARGET-10.0},$host in
-	10.0,*86*-darwin8*|10.0,*-darwin[91]*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
+    *-darwin*)
+      # darwin 5.x (macOS 10.1) onwards we only need to adjust when the
+      # deployment target is forced to an earlier version.
+      case ${MACOSX_DEPLOYMENT_TARGET-UNSET},$host in
+	UNSET,*-darwin[89]*|UNSET,*-darwin[12][0123456789]*)
+	  ;;
 	10.[012][,.]*)
-	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress' ;;
-	10.*)
-	  _lt_dar_allow_undefined='${wl}-undefined ${wl}dynamic_lookup' ;;
-      esac
+	  _lt_dar_allow_undefined='${wl}-flat_namespace ${wl}-undefined ${wl}suppress'
+	  ;;
+	*)
+	  ;;
+     esac
     ;;
   esac
     if test "$lt_cv_apple_cc_single_mod" = "yes"; then