[clang] [FMV] Emit the resolver along with the default version definition. (PR #84405)

[Alexandros Lamprineas via cfe-commits]

labrinea wrote:

The key takeaway from my conversation with @DanielKristofKiss was that it is important for Function Multi Versioning to work even when the default target attribute is omitted. It was quite a headache to get this working in clang, but the latest revision supports the desired behavior. It also fixes the previously discovered bug I had mentioned in the test file.

https://github.com/llvm/llvm-project/pull/84405