[llvm] Cpu features cross platform (PR #205447)

[Lang Hames via llvm-commits]

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

None of those comments are blocking -- if you're happy to fix up pre-merge go for it (you needn't wait for a follow-up review before merging). Otherwise I'm happy for you to fix these in-tree with follow-up PRs if you prefer.

https://github.com/llvm/llvm-project/pull/205447