While tracking down gcc 4.7.1 issues I tried a -O1 build,
and got uninitialized variable warnings. None of them is
real, and at -O3 the compiler can figure out that the variables
are never actually used uninitialized.
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.
aalexandre