[llvm] [LoopFlatten] Invalidate SCEV on each widening (PR #211819)

[Arda Serdar Pektezol via llvm-commits]

pektezol wrote:

I had an MLIR failure before updating the fork and rebasing to base. Now I see clang analysis failures. I believe these are unrelated. Review points are addressed, MR title and description updated.

https://github.com/llvm/llvm-project/pull/211819