GitLab

This is installed already on build.gnome.org, and we don't really need
more that it to build the SDK, so we favour the smaller setuid helper
here.

Now that we have some basic gstreamer plugins the build succeeds.

We don't ship alsa or cdparanoia plugins, as they make little sense
in a container.

Libvisual is also disabled, as its not in yocto. Maybe we should add it though?
Does things use it?

This adds liberation-fonts, gnu-free-fonts, and the
google caladea & carlito fonts. This way we have metric compatible
fonts for the MS core fonts, and a font with a lot of coverage.

They would be cleaned the next time anyway, but this makes it clean
up for the last build. In particular this is important if build is
on a tmpfs

Makes fontconfig look for fonts in /self, and in /run/host.
Reads an optional config file in /self.
Moves the cache-dir out of /var, so it can be in the image.

This moves "root" and "var" into "build" subdir, allowing you
to create a symlink somewhere (such as /tmp) to put these.

If packages/.ccache exists, set up the build to use it

This is basically the same as the above, except some old leftovers
from gnome-continuous are removed and it is a pure layer.
It also bumps the yocto dependency to the latest 1.7 version, and
makes it very easy to bump it in the future.