Update a number of things to make optionally generating the parser at
build time possible. @sgolemon will add the OSS pieces of this in a
separate commit.
It's enabled if the HPHP_TRACE_FILE is "/dev/stdout" or
"/dev/stderr" and also isatty(), or you can set HPHP_TRACE_TTY in your
environment to override it (e.g. if you like to pass to less -R).
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.
Owen Yamauchi