[compiler-rt] [compiler-rt][CMake] Pass all flags to _Float16 try-compile (PR #133952)

[Evan Wilde via llvm-commits]

etcwilde wrote:

> Unrelated to this change but I see string(REPLACE ";" " " _TARGET_${arch}_CFLAGS "${TARGET_${arch}_CFLAGS}") below, which I think could just be dropped and we use CMAKE_REQUIRED_FLASG instead?

Even better, it looks like `check_compile_definition` implicitly adds `CMAKE_REQUIRED_FLAGS`:
https://github.com/llvm/llvm-project/blob/1edb6b0af1c47f88aa5c230a1a2b769eeb3c30aa/compiler-rt/cmake/Modules/CompilerRTUtils.cmake#L94-L103

I've dropped adding those arguments entirely and it's only adding `CMAKE_C_FLAGS`.

https://github.com/llvm/llvm-project/pull/133952