[X86] Don't use constant condition for select instruction when testing masking ops.

[X86] Don't use constant condition for select instruction when testing masking ops.

We should be able to fold constant conditions by converting to shuffles, but fixing that would break these tests in their current form. Since they are really trying to test masking ops, add a non-constant mask to the selects.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315848 91177308-0d34-0410-b5e6-96231b3b80d8