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

[Ryan Prichard via cfe-commits]

rprichard wrote:

> I was waiting for your recent PRs to land, but the android failures seem to persist even after them.

Yeah that's also what I noticed. My PRs were aimed at getting the Android Dockerfile buildable again, but once it was buildable, the feature testing failed.

It _seemed_ that after this PR, the CMake feature test for a flag `-foo` wasn't even passing `-foo` to the Clang driver, but maybe I was reading too much into the CMake log output. It definitely wasn't handling the bootstrapping situation correctly -- it was trying to detect whether the driver supported `-nostdlib++` and concluded that it didn't, because it couldn't link an executable using `-lc++` (because libc++ hadn't been built yet).

My suspicion was that this PR broke CMake feature testing for any cross-compiled configurations.


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