Only in RepoAuthoritative mode, where units can't be
deallocated. I have a semi-reproducable bug where a unit's m_bc
region is getting corrupted (only occasionally in perflab).
Presumably moving it out of the malloc'd heap will make the bug
corrupt something else, so this probably doesn't really help much, but
it seemed like having a separate region for some cold, read-only,
process-lifetime metadata might make sense.
This should only happen if there's a bug in our code and the
child process crashes, or if one gets killed by the OOM killer. In
either case, it's probably not safe for the parent process to continue
uninterrupted, so shut down.
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.
jdelong