[clang] [FMV] Allow target version definitions in any order. (PR #83887)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

I appreciate there's some code repetition between `CheckTargetCausesMultiVersioning` and `CheckMultiVersionAdditionalDecl`. Perhaps they deserve some refactoring in a separate patch. Please advise if you have any suggestions for moving the fix elsewhere.

https://github.com/llvm/llvm-project/pull/83887