The libcore build currently fails with an error message "execvp: ar:
Argument list is too long". This seems to be happening because we have
too many environment variables set. This revision addresses the issue
by unsetting more of the environment variables that aren't needed.
libcore build succeededs
DiffCamp Revision: 164548
Reviewed By: mwilliams
CC: mwilliams, hphp-diffs@lists