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

[Jack Styles via cfe-commits]

Stylie777 wrote:

> 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.
+1 to this, I agree this should be done in a separate patch.

Thanks all for your reviews.

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