Pretty self-explanatory. I took out the 32-bit compatibility stuff
because we're pretty far away from being able to support 32-bit
platforms (the open source build explicitly checks and fails on 32-bit).
On non-x64 platforms, we'll fall back to calling uname(). As far as I
can tell, ARM doesn't have a "processor name" facility like x86 does,
but if we find one, we can add support for it here.
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.