[llvm] [SelectionDAG]: Deduce KnownNeverZero from SMIN and SMAX (PR #85722)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

Please can you rebase - I've added better target coverage to known-never-zero.ll

https://github.com/llvm/llvm-project/pull/85722