Make bitcast, extractelement, and insertelement considered
cheap for speculation.

This helps more branches into selects. On R600,
vectors are cheap and anything that helps
remove branches is very good.

I don't know why this isn't using the TTI for this cost
calculation.
Add failing control flow test
Add somewhat processed testcase copy that fails on SI
Add simplest branch testcase that still fails
Add failing basic loop test
Add infinite loop test.

It is missing the branch entirely.
xxx - work on control flow unhandled error
XXX - More unhandled assert work