[llvm] [CodeGen] Avoid ambiguous Register comparison in C++20; NFC (PR #205814)

[Sven van Haastregt via llvm-commits]

svenvh wrote:

> I wonder if there's a reason `ForwardedRegWorklist` uses uint64_t for the register rather than just `Register`... it seems like that would probably be a reasonable solution.

Thanks, I hadn't thought of that but it seems like that works too.  I've updated the patch.

https://github.com/llvm/llvm-project/pull/205814