[Darwin][CompilerRT] Set compiler ID to 'Clang' for Compiler RT Tests

This patch restores previous behavior we relied on. Even when the Compiler ID is set to AppleClang, we expect Compiler RT Tests to use Clang as the compiler ID. This impacts various make and lit commands.

Caused by: https://github.com/llvm/llvm-project/pull/117812/files

rdar://141548700

Author: thetruestblue

compiler-rt/cmake/base-config-ix.cmake

@@ -79,7 +79,12 @@ endif()
 
 get_filename_component(_test_compiler_name "${COMPILER_RT_TEST_COMPILER}" NAME)
 if("${COMPILER_RT_TEST_COMPILER}" STREQUAL "${CMAKE_C_COMPILER}")
-  set(COMPILER_RT_TEST_COMPILER_ID "${CMAKE_C_COMPILER_ID}")
+  if ("${CMAKE_C_COMPILER}" STREQUAL "AppleClang")
+    # Compiler-rt tests expect compiler ID 'Clang' for AppleClang.
+    set(COMPILER_RT_TEST_COMPILER_ID Clang)
+  else()
+    set(COMPILER_RT_TEST_COMPILER_ID "${CMAKE_C_COMPILER_ID}")
+  endif()
 elseif("${_test_compiler_name}" MATCHES "clang.*")
   set(COMPILER_RT_TEST_COMPILER_ID Clang)
 elseif("${_test_compiler_name}" MATCHES "cl.exe$")