make install
Installs hhvm and systemlib.php to CMAKE_INSTALL_PREFIX/bin
To override the default location define it during cmake:
cmake -DCMAKE_INSTALL_PREFIX=/usr/hphp .
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.