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

[Luke Lau via llvm-commits]

lukel97 wrote:

I've swept llvm-test-suite and SPEC CPU 2017 on AArch64/X86/RISC-V at -O3 with `-combiner-topological-sorting` and there was no difference to any codegen, so I'm 99% sure the patterns are dead

I've updated the aarch64 tests to be in the form the middle end spits out. There's already tests for the correlated value propagation transform in `test/Transforms/CorrelatedValuePropagation/min-max.ll` under `test_smax_to_umax_nneg` and friends. I don't think we can add a phaseordering test since that directory only tests middle end passes w/ `opt`.

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