During vector shuffle lowering, we sometimes commute a vector shuffle to try

During vector shuffle lowering, we sometimes commute a vector shuffle to try
to match MOVL (movss, movsd, etc.). Don't forget to commute it back and try
unpck* and shufp* if that doesn't pan out.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31186 91177308-0d34-0410-b5e6-96231b3b80d8