This is a rather mechanical refactor that uses references (&) rather than pointers (*) for parameters that are not permitted to ever be given null arguments. In effect, the onus for checking null pointers is shifted from the callee to the caller. The & type annotation makes it clear that the callee is not prepared to deal with a null pointer.
This change is mostly for FB internal organizational reasons.
Building is not effected beyond the fact that the target now
lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.