Allow fork fission to not take in an explicit data label - in this case, implicitly the fission point is between the parallel section and the reduction cycle (this is the most common case).
CleanMonoidReduces pass which makes outer forks around monoid reductions more easily parallelizable after fission.
Fix GCM behavior w/ primitive constants / undefs.
Make SimplifyCFG more aggressive with removing reduces (motivated by fission).
Add UnforkifyOne pass, which only unforkifies the first loop it sees - useful for unforkifying outer loops.
Multi-core dot product test that uses a bunch of the stuff in this MR.
