[llvm] [CloneFunciton] Optimize PHI incoming value removal using reverse iteration (NFC) (PR #171955)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

This case is a bit more iffy, but should probably also use removeIncomingValueIf()? It may modify the incoming value in case it's not removed, but I believe that should be safe.

https://github.com/llvm/llvm-project/pull/171955