[InstCombine] Fold (min/max ~X, Y) -> ~(max/min X, ~Y) when Y is freely invertible

If the ~X wasn't able to simplify above the max/min, we might be able to simplify it by moving it below the max/min.

I had to modify the ~(min/max ~X, Y) transform to prevent getting stuck in a loop when we saw the new ~(max/min X, ~Y) before the ~Y had been folded away to remove the new not.

Differential Revision: https://reviews.llvm.org/D51398

llvm-svn: 341674