Do not setup homebrew until after XCode is installed

The homebrew installer attempts to install XCode, but it uses the GUI to
do so. This (obviously) breaks a headless Chef install where no GUI is
present.
Compile gettext from source

We cannot install gettext from homebrew (it's too old or something
prevents it from working with git), so we need to compile from source.
It is also worth noting that the "version" gettext reports does not
include the last digit (0.18.3.2 -> 0.18.3).
Fix failing specs