[llvm] [RegisterCoalescer] Fix reuse of instruction pointers (PR #73519)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

Needs test.

I'm not a fan of try to remove from the worklist after the fact, and then try the second worklist. We know from the copy which list it was in, whether it was local or not. 

I've also never trusted this managing pointers to instructions that have already been deleted scheme. 


https://github.com/llvm/llvm-project/pull/73519