[llvm] [VPlan] Don't use the legacy cost model for loop conditions (PR #156864)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

thanks for the altet update, checked the latest verison, but I think we still effectively always disable the assertion now, because the original exiting condition will get removed and then we won't find a recipe matching the compare, which so planContainsAdditionalSimplification will always return true

https://github.com/llvm/llvm-project/pull/156864