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

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

simplifySetCCWithCTPOP appears to use isKnownNeverZero for the `(ctpop x) eq/ne 1 --> (x & x-1) eq/ne 0` fold - maybe try that?

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