[InstSimplify][NFC] Tests for skipping 'div-by-0' checks before inverted @llvm.umul.with.overflow

It would be already handled by the non-inverted case if we were hoisting
the `not` in InstCombine, but we don't (granted, we don't sink it
in this case either), so this is a separate case.

llvm-svn: 366801