NewGVN: This patch makes memory congruence work for all types of

NewGVN: This patch makes memory congruence work for all types of
memorydefs, not just stores.  Along the way, we audit and fixup issues
about how we were tracking memory leaders, and improve the verifier
to notice more memory congruency issues.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299682 91177308-0d34-0410-b5e6-96231b3b80d8