[Statepoints] Add test cases around vectors and stablize test

Unlike my comment in 257022 said, it turns out we do handle constant vectors in the statepoint lowering, but only because SelectionDAG doesn't actually produce constants for them.  Add a couple of tests which show this working.

Also, add a triple to the same test file to hopefully fix a failing bot.

It turns out we do han

llvm-svn: 257025