[llvm] [LV] Use frozen start value for FindLastIV if needed. (PR #132691)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

Updated to current main, so now only the PR changes should be included.

Updated the PR to only freeze when vectorizing the epilogue, as this is the only case where it should be needed

https://github.com/llvm/llvm-project/pull/132691