[X86] Combine fminnum/fmaxnum with non-nan operand to fmin/fmax

[X86] Combine fminnum/fmaxnum with non-nan operand to fmin/fmax

If we have a known non-nan operand, place it in the second operand
of fmin/fmax that is returned if either operand is nan.

Differential Revision: https://reviews.llvm.org/D62448

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@361704 91177308-0d34-0410-b5e6-96231b3b80d8