Revert "[CMake] Unify llvm_check_linker_flag and llvm_check_compiler_linker_flag"

[fsb4000]

Summary

libc++ clang-cl tests failed after that commit

Look at https://buildkite.com/llvm-project/libcxx-ci/builds/20490

cmake/Modules/LLVMCheckCompilerLinkerFlag.cmake

-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()
 
-  # 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} ${flag}")
+  # If testing a flag with check_c_compiler_flag, it gets added to the compile
+  # command only, but not to the linker command in that test. If the flag
+  # is vital for linking to succeed, the test would fail even if it would
+  # have succeeded if it was included on both commands.
+  #
+  # Therefore, try adding the flag to CMAKE_REQUIRED_FLAGS, which gets
+  # added to both compiling and linking commands in the tests.
+
+  cmake_push_check_state()
+  set(CMAKE_REQUIRED_FLAGS "${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()
+  cmake_pop_check_state()
+endfunction()