[compiler-rt] [llvm] [LLVM][compiler-rt] Fix build with LLVM_USE_SANITIZER=Undefined (PR #120006)

[Jon Roelofs via llvm-commits]

================
@@ -1064,7 +1064,8 @@ if(LLVM_USE_SANITIZER)
   if (LLVM_USE_SANITIZE_COVERAGE)
     append("-fsanitize=fuzzer-no-link" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
   endif()
-  if (LLVM_USE_SANITIZER MATCHES ".*Undefined.*")
+  if (LLVM_USE_SANITIZER MATCHES ".*Undefined.*" AND CMAKE_C_COMPILER_ID MATCHES "Clang" AND
+		                                     CMAKE_CXX_COMPILER_ID MATCHES "Clang")
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jroelofs wrote:

ohh, I think it would help a lot to put that concept in a variable, e.g:

```
check_cxx_compiler_flag(-fsanitize-blacklist=${IGNORELIST_FILE} COMPILER_RT_CXX_SUPPORTS_FSANITIZE_BLACKLIST)
```

instead of tying this to the specific compiler.

https://github.com/llvm/llvm-project/pull/120006