[MemorySSA] Fix invariant.group test and add new

Summary:
This test had a bug: !llvm.invariant.group instead
of !invariant.group.

Also add some new test for future development.
All tests passes, when MSSA will support invariant.group
only the lines with FIXIT should be changed.

Reviewers: dberlin, george.burgess.iv

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28969

llvm-svn: 292730