Extend the test coverage in combine-vec-shuffle-2.ll adding some negative tests.

Add test cases where we don't expect to trigger the combine optimizations
introduced at revision 212748.

No functional change intended.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212756 91177308-0d34-0410-b5e6-96231b3b80d8