From: Jory A. Pratt <anarchy@gentoo.org>

CFLAGS must contain -fPIC when checking the linker

https://bugs.gentoo.org/show_bug.cgi?id=607350

diff --git a/build/autoconf/compiler-opts.m4 b/build/autoconf/compiler-opts.m4
--- a/build/autoconf/compiler-opts.m4
+++ b/build/autoconf/compiler-opts.m4
@@ -261,23 +261,26 @@ fi
 
 MOZ_ARG_ENABLE_BOOL(pie,
 [  --enable-pie           Enable Position Independent Executables],
     MOZ_PIE=1,
     MOZ_PIE= )
 
 if test "$GNU_CC$CLANG_CC" -a -n "$MOZ_PIE"; then
     AC_MSG_CHECKING([for PIE support])
+    _SAVE_CFLAGS=$CFLAGS
+    CFLAGS="$CFLAGS -fPIC"
     _SAVE_LDFLAGS=$LDFLAGS
     LDFLAGS="$LDFLAGS $DSO_PIC_CFLAGS -pie"
     AC_TRY_LINK(,,AC_MSG_RESULT([yes])
                   [MOZ_PROGRAM_LDFLAGS="$MOZ_PROGRAM_LDFLAGS -pie"],
                   AC_MSG_RESULT([no])
                   AC_MSG_ERROR([--enable-pie requires PIE support from the linker.]))
     LDFLAGS=$_SAVE_LDFLAGS
+    CFLAGS=$_SAVE_CFLAGS
 fi
 
 AC_SUBST(MOZ_PROGRAM_LDFLAGS)
 
 dnl ASan assumes no symbols are being interposed, and when that happens,
 dnl it's not happy with it. Unconveniently, since Firefox is exporting
 dnl libffi symbols and Gtk+3 pulls system libffi via libwayland-client,
 dnl system libffi interposes libffi symbols that ASan assumes are in