[llvm] [ConstraintElim] Try to get induction step/start/flags from IR (NFC-ish) (PR #209284)

[Antonio Frighetto via llvm-commits]

https://github.com/antoniofrighetto approved this pull request.

LGTM, assuming we are fine trading potential precision on flags on AddRecs that SCEV might have previously inferred for compile-time improvement (tracker seems unavailable right now?).

https://github.com/llvm/llvm-project/pull/209284