This reduces CPU instruction count by about 0.2%, has negligible impact on other metrics. Implementation has been changed a but upon discussion with @mwilliams to account for circular destruction. The question remains open whether this should be in before or after rooting out hphpc, but on the other hand we gotta do what we gotta do to move forward.
Array is already a SmartPtr, wrapping it in another is pointless.
Except it turns out that there are include dependencies preventing
us from using Array here. Use boost::intrusive_ptr to wrap an
ArrayData instead.
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.
mwilliams