[llvm] [LoopInterchange] Prevent from undoing its own transformation (PR #127473)

[Michael Kruse via llvm-commits]

https://github.com/Meinersbur commented:

Could you please moved the refactorings/cleanups out of this patch? I am still confused what `CostMap` actually does.

https://github.com/llvm/llvm-project/pull/127473