[InstCombine] allow sinking fneg operands through an FP min/max

[InstCombine] allow sinking fneg operands through an FP min/max

Fundamentally/generally, we should not have to rely on bailouts/crippling of
folds. In this particular case, I think we always recognize the inverted
predicate min/max pattern, so there should not be any loss of optimization.
Codegen looks better because we are eliminating an fneg.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@360180 91177308-0d34-0410-b5e6-96231b3b80d8