[clang] [compiler-rt] [libcxx] [libunwind] [llvm] [openmp] [cmake] switch to CMake's native `check_{compiler,linker}_flag` (PR #96171)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson commented:

Since I believe the CMake minimum version supports this, I don't see why we shouldn't submit this cleanup. Whether to change the flag detection logic can be a separate discussion IMO.

https://github.com/llvm/llvm-project/pull/96171