[libc-commits] [libc] [libc] Include CheckCXXCompilerFlag when checking compiler features (PR #118862)

[Joseph Huber via libc-commits]

https://github.com/jhuber6 requested changes to this pull request.

This should probably just go at the top level since it's used here
```
startup/linux/CMakeLists.txt
77:check_cxx_compiler_flag("-r" LIBC_LINKER_SUPPORTS_RELOCATABLE)

cmake/modules/CheckCompilerFeatures.cmake
136:check_cxx_compiler_flag("-ftrivial-auto-var-init=pattern" LIBC_CC_SUPPORTS_PATTERN_INIT)
139:check_cxx_compiler_flag("-nostdlib++" LIBC_CC_SUPPORTS_NOSTDLIBPP)
142:check_cxx_compiler_flag("-nostdlibinc" LIBC_CC_SUPPORTS_NOSTDLIBINC)

cmake/modules/prepare_libc_gpu_build.cmake
44:  check_cxx_compiler_flag(-mcpu=native PLATFORM_HAS_GPU)
46:  check_cxx_compiler_flag(-march=native PLATFORM_HAS_GPU)
```

https://github.com/llvm/llvm-project/pull/118862