[llvm] MachineScheduler: Improve instruction clustering (PR #137784)

[via llvm-commits]

ruiling wrote:

Hi @mysterymath, The change might increase the compile time because of the `contains()` call. But I think it should not cause too much drop as the set is usually small. Anyway, I have changed the way to do the cluster check in #150884 . It should help the compile time.

https://github.com/llvm/llvm-project/pull/137784