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

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

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

We could fix it by adding a case for armv7 on Darwin in `ARM::getARMCPUForArch`, which would allow getting rid of that special case here. But as we currently have the special cases for Windows/Darwin here, I would rather prefer to not touch that within this change, but do such cleanup in a later separate PR.

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