[clang] [NFC][Clang][FMV] Refactor sema checking of target_version/clones attributes. (PR #149067)

[Tomas Matheson via cfe-commits]

https://github.com/tmatheson-arm commented:

LGTM, just lots of style comments. Most of them probably apply to the original code too so feel free to address them in a follow up if you prefer.

https://github.com/llvm/llvm-project/pull/149067