Refactor linux build tools into a single dep, sprucing up the 'provides'. (And fixing the yum packages, I think. Awkward.)
Consolidate xcode tools deps into a single external with an updated 'provides'.
Use long options in PacmanHelper.
Fix the log message when syncing (installing) packages via pacman.
Use #pkg_cmd in PacmanHelper#has_pkg?.
Use --noprogressbar when syncing packages via pacman.
Use the pacman exit code in PacmanHelper#has_pkg?.