[llvm] [VPlan] Simplify VPPhi with all-equal incoming (PR #157414)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

It looks like there is a new crash with the change the reproducer from https://llvm.godbolt.org/z/rsavGTGhK crashes

https://github.com/llvm/llvm-project/pull/157414