[x86] add tests for vector select-of-constants; NFC

We've discussed canonicalizing to this form in IR, so the backend
should be prepared to lower these in ways better than what we see
here in most cases.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@311103 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed