[GVN] Fix last crasher w/non-integral pointers

[GVN] Fix last crasher w/non-integral pointers

Same case as for memset and memcpy, but this time for clobbering stores and loads.  We still can't allow coercion to or from non-integrals, regardless of the transform.

Now that I'm done the whole little sequence, it seems apparent that we'd entirely missed reasoning about clobbers in the original GVN support for non-integral pointers.

My appologies, I thought we'd upstreamed all of this, but it turns out we were still carrying a downstream hack which hid all of these issues.  My chanks to Cherry Zhang for helping debug.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354407 91177308-0d34-0410-b5e6-96231b3b80d8