cmake PLATFORM_HAS_GPU examples

Lewuathe/mlir-hello thirdparty/llvm-project/libc/cmake/modules/prepare_libc_gpu_build.cmake :44 

check_cxx_compiler_flag(-mcpu=native PLATFORM_HAS_GPU)

Lewuathe/mlir-hello thirdparty/llvm-project/libc/cmake/modules/prepare_libc_gpu_build.cmake :46 

check_cxx_compiler_flag(-march=native PLATFORM_HAS_GPU)

Lewuathe/mlir-hello thirdparty/llvm-project/libc/cmake/modules/prepare_libc_gpu_build.cmake :63 

elseif(PLATFORM_HAS_GPU)