[X86] Use min/max to optimze unsigend vector comparison on X86

Use PMIN/PMAX for UGE/ULE vector comparions to reduce the number of required
instructions. This trick also works for UGT/ULT, but there is no advantage in
doing so. It wouldn't reduce the number of instructions and it would actually
reduce performance.

Reviewer: Ben

radar:5972691



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186432 91177308-0d34-0410-b5e6-96231b3b80d8