[clang] [Clang][ARM] Ensure FPU Features are parsed when targeting `cc1as` (PR #134612)

[David Green via cfe-commits]

https://github.com/davemgreen approved this pull request.

The other thing this patch does is bring the preprocessor features for -march=armv8.1-m in line with the assembly features. It was previously enabling __ARM_VFPV2__ but not allowing vfpv2 instructions.

I'm still not sure about the Win/Darwin part, but otherwise LGTM.

https://github.com/llvm/llvm-project/pull/134612