InstSimplify: Optimize away useless unsigned comparisons

Code like X < Y && Y == 0 should always be folded away to false.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223583 91177308-0d34-0410-b5e6-96231b3b80d8
I didn't intend to commit this change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223584 91177308-0d34-0410-b5e6-96231b3b80d8