[llvm] [LoopInterchange] Fix handling of PHI which refers to another PHI (PR #194364)

[Sjoerd Meijer via llvm-commits]

https://github.com/sjoerdmeijer approved this pull request.

LGTM.

Maybe wait a day in case @Meinersbur want to have a look too.

https://github.com/llvm/llvm-project/pull/194364