Gentoo uses GNU awk by default, but since we are using Busybox for the
rest of the userspace utilities, it makes sense to use awk from Busybox
as well.
Instead of copying the Portage configuration files to `/etc/portage` and
`/usr/${target}/etc/portage`, the build scripts now use the
configuration directories from the source directory. This avoids issues
with changes (especially removal of files) getting propagated to the
actual configuration paths.
