[llvm] [InstCombine] Use `m_NotForbidPoison` when folding `(X u< Y) ? -1 : (~X + Y) --> uadd.sat(~X, Y)` (PR #114345)

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

LGTM although I have trouble believing this is the only place we have this type of bug.

https://github.com/llvm/llvm-project/pull/114345