Revert "[CMake] Unify llvm_check_linker_flag and llvm_check_compiler_linker_flag"

This reverts commit 55e65ad.

Author: petrhosek

cmake/Modules/LLVMCheckCompilerLinkerFlag.cmake

@@ -1,28 +1,35 @@
-include(CheckLinkerFlag OPTIONAL)
+include(CMakePushCheckState)
 
-if (COMMAND check_linker_flag)
-  macro(llvm_check_compiler_linker_flag)
-    check_linker_flag(${ARGN})
-  endmacro()
-else()
-  # Until the minimum CMAKE version is 3.18
+include(CheckCompilerFlag OPTIONAL)
 
+if(NOT COMMAND check_compiler_flag)
+  include(CheckCCompilerFlag)
   include(CheckCXXCompilerFlag)
+endif()
+
+function(llvm_check_compiler_linker_flag lang flag out_var)
+  # If testing a flag with check_c_compiler_flag, it gets added to the compile
+  # command only, but not to the linker command in that test. If the flag
+  # is vital for linking to succeed, the test would fail even if it would
+  # have succeeded if it was included on both commands.
+  #
+  # Therefore, try adding the flag to CMAKE_REQUIRED_FLAGS, which gets
+  # added to both compiling and linking commands in the tests.
 
-  # cmake builtin compatible, except we assume lang is C or CXX
-  function(llvm_check_compiler_linker_flag lang flag out_var)
-    cmake_policy(PUSH)
-    cmake_policy(SET CMP0056 NEW)
-    set(_CMAKE_EXE_LINKER_FLAGS_SAVE ${CMAKE_EXE_LINKER_FLAGS})
-    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${flag}")
+  cmake_push_check_state()
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${flag}")
+  if(COMMAND check_compiler_flag)
+    check_compiler_flag("${lang}" "" ${out_var})
+  else()
+    # Until the minimum CMAKE version is 3.19
+    # cmake builtin compatible, except we assume lang is C or CXX
     if("${lang}" STREQUAL "C")
       check_c_compiler_flag("" ${out_var})
     elseif("${lang}" STREQUAL "CXX")
       check_cxx_compiler_flag("" ${out_var})
     else()
       message(FATAL_ERROR "\"${lang}\" is not C or CXX")
     endif()
-    set(CMAKE_EXE_LINKER_FLAGS ${_CMAKE_EXE_LINKER_FLAGS_SAVE})
-    cmake_policy(POP)
-  endfunction()
-endif()
+  endif()
+  cmake_pop_check_state()
+endfunction()

runtimes/CMakeLists.txt

@@ -142,11 +142,8 @@ endif()
 # Check for -nostdlib++ first; if there's no C++ standard library yet,
 # all check_cxx_compiler_flag commands will fail until we add -nostdlib++
 # (or -nodefaultlibs).
-# TODO: Switch to check_linker_flag after raise the minimum CMake version past 3.14.
-check_cxx_compiler_flag(-nostdlib++ CXX_SUPPORTS_NOSTDLIBXX_FLAG)
+llvm_check_compiler_linker_flag(CXX "-nostdlib++" CXX_SUPPORTS_NOSTDLIBXX_FLAG)
 if (CXX_SUPPORTS_NOSTDLIBXX_FLAG)
-  # TODO: This is link only flag and should be added to CMAKE_REQUIRED_LINK_OPTIONS
-  # but that's only supported since CMake 3.14.
   set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdlib++")
 endif()
 check_cxx_compiler_flag(-nostdinc++ CXX_SUPPORTS_NOSTDINCXX_FLAG)