Add some transforms of the kind X-Y>X -> 0>Y which are valid when there is no

Add some transforms of the kind X-Y>X -> 0>Y which are valid when there is no
overflow.  These subsume some existing equality transforms, so zap those.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125843 91177308-0d34-0410-b5e6-96231b3b80d8