[llvm] [DAG] Don't detect flippable signs in MinMax matchers (PR #220527)

[Simon Pilgrim via llvm-commits]

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

OK, let's go with this - I'm still worried we'll end up back-pedaling but we'll deal with that if we have a better case.

https://github.com/llvm/llvm-project/pull/220527