[clang] [FMV][AArch64][clang] Emit fmv-features metadata in LLVM IR. (PR #118544)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

> A motivating example might be target_version("simd+dotprod") and target_version("sve"): when sve is available we should pick that version, but the current rule prioritizes the number of attribute-specified features over their overall weight.

I agree about this. As I said we will adress the priorities and selection algorithm separately. However in the example I am mentioning the problem arises once we mix target-features from the cmdline with fmv-features. So we need separate metadata. I was thinking whether it makes sense to expand the fmv dependecies before we store them in metadata but I think it's not necessary. We can perform this step later.

https://github.com/llvm/llvm-project/pull/118544