[llvm] [AMDGPU][SIInsertWaitcnts][NFC] Introduce Counter class (PR #190271)

[Shilei Tian via llvm-commits]

shiltian wrote:

> Given that these patches need to remain small, some intermediate state is necessary and will be cleaned up in the follow-up patches. This is not uncommon and should not be a blocker.

I think we are asking is a stack of PRs, instead of some commits, nor a giant commit (we definitely don't want that). The advantage of a stack is, we can clearly see the path towards what you envision such that it is easier to see how these intermediate states play the role in the long run.

https://github.com/llvm/llvm-project/pull/190271