Fix shift by constants for vector.

ashr <N x iM>, <N x iM> M -> undef

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206045 91177308-0d34-0410-b5e6-96231b3b80d8
Add some CHECKs to this testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206046 91177308-0d34-0410-b5e6-96231b3b80d8