[clang] [llvm] [NFC][clang][FMV][TargetInfo] Refactor API for FMV feature priority. (PR #116257)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

I THINK this looks right?  X86 code ownership should probably make sure this is still correct for x86.  @phoebewang as the defacto owner of x86 function multiversioning priority checking.

https://github.com/llvm/llvm-project/pull/116257