--- cpp/cmake_modules/DefineOptions.cmake
+++ cpp/cmake_modules/DefineOptions.cmake
@@ -76,7 +76,7 @@ macro(define_option_string name description default)
 endmacro()
 
 # Top level cmake dir
-if("${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
+if(1)
   #----------------------------------------------------------------------
   set_option_category("Compile and link")
 
--- cpp/cmake_modules/ThirdpartyToolchain.cmake
+++ cpp/cmake_modules/ThirdpartyToolchain.cmake
@@ -854,7 +854,7 @@ if(ARROW_WITH_SNAPPY)
     # location.
     # https://bugzilla.redhat.com/show_bug.cgi?id=1679727
     # https://src.fedoraproject.org/rpms/snappy/pull-request/1
-    find_package(Snappy QUIET HINTS "${CMAKE_ROOT}/Modules/")
+    find_package(Snappy REQUIRED)
     if(NOT Snappy_FOUND)
       find_package(SnappyAlt)
     endif()
@@ -866,7 +866,7 @@
   elseif(Snappy_SOURCE STREQUAL "SYSTEM")
     # SnappyConfig.cmake is not installed on Ubuntu/Debian
     # TODO: Make a bug report upstream
-    find_package(Snappy HINTS "${CMAKE_ROOT}/Modules/")
+    find_package(Snappy REQUIRED)
     if(NOT Snappy_FOUND)
       find_package(SnappyAlt REQUIRED)
     endif()
@@ -1139,8 +1139,8 @@
     build_gflags()
   elseif(gflags_SOURCE STREQUAL "SYSTEM")
-    # gflagsConfig.cmake is not installed on Ubuntu/Debian
-    # TODO: Make a bug report upstream
-    find_package(gflags ${ARROW_GFLAGS_REQUIRED_VERSION})
+    find_package(gflags REQUIRED)
+    add_library(gflags-shared INTERFACE)
+    target_link_libraries(gflags-shared INTERFACE gflags::gflags)
     if(NOT gflags_FOUND)
       find_package(gflagsAlt ${ARROW_GFLAGS_REQUIRED_VERSION} REQUIRED)
     endif()
@@ -1329,6 +1329,6 @@ macro(build_protobuf)
 endmacro()
-
 if(ARROW_WITH_PROTOBUF)
+  find_package(Protobuf REQUIRED)
   if(ARROW_WITH_GRPC)
     # gRPC 1.21.0 or later require Protobuf 3.7.0 or later.
     set(ARROW_PROTOBUF_REQUIRED_VERSION "3.7.0")
@@ -1365,9 +1365,9 @@ if(ARROW_WITH_PROTOBUF)
     set(ARROW_PROTOBUF_LIBPROTOC arrow::protobuf::libprotoc)
   else()
     if(NOT TARGET protobuf::libprotoc)
+      set(Protobuf_PROTOC_LIBRARY protoc)
       if(PROTOBUF_PROTOC_LIBRARY AND NOT Protobuf_PROTOC_LIBRARY)
-        # Old CMake versions have a different casing.
-        set(Protobuf_PROTOC_LIBRARY ${PROTOBUF_PROTOC_LIBRARY})
+        set(Protobuf_PROTOC_LIBRARY protoc)
       endif()
       if(NOT Protobuf_PROTOC_LIBRARY)
         message(FATAL_ERROR "libprotoc was set to ${Protobuf_PROTOC_LIBRARY}")
@@ -1802,7 +1802,7 @@ if(ARROW_WITH_RAPIDJSON)
   elseif(RapidJSON_SOURCE STREQUAL "SYSTEM")
     # Fedora packages place the package information at the wrong location.
     # https://bugzilla.redhat.com/show_bug.cgi?id=1680400
-    find_package(RapidJSON ${ARROW_RAPIDJSON_REQUIRED_VERSION} HINTS "${CMAKE_ROOT}")
+    find_package(RapidJSON REQUIRED)
     if(RapidJSON_FOUND)
       set(RAPIDJSON_INCLUDE_DIR ${RAPIDJSON_INCLUDE_DIRS})
     else()
@@ -2088,7 +2088,7 @@ if(ARROW_WITH_BZ2)
                           PROPERTIES IMPORTED_LOCATION "${BZIP2_LIBRARIES}"
                                      INTERFACE_INCLUDE_DIRECTORIES "${BZIP2_INCLUDE_DIR}")
   endif()
-  include_directories(SYSTEM "${BZIP2_INCLUDE_DIR}")
+  include_directories(SYSTEM "${BZip2_INCLUDE_DIR}")
 endif()
 
 macro(build_utf8proc)
--- cpp/cmake_modules/SetupCxxFlags.cmake
+++ cpp/cmake_modules/SetupCxxFlags.cmake
@@ -188,7 +188,7 @@
 message(STATUS "Arrow build warning level: ${BUILD_WARNING_LEVEL}")
 
 macro(arrow_add_werror_if_debug)
-  if("${CMAKE_BUILD_TYPE}" STREQUAL "DEBUG")
+  if(0)
     # Treat all compiler warnings as errors
     if(MSVC)
       set(CXX_COMMON_FLAGS "${CXX_COMMON_FLAGS} /WX")