This builds glib using meson/ninja/ccache with mingw-w64 on a Windows
machine.
The CI scripts expect a gitlab runner to exist with the "win32" tag
which uses the default "cmd" shell by default.
Before running the tests pacman is invoked to update the system
(potentially including bash etc, thus the extra step)
Then a login shell is started with CHERE_INVOKING to not change the
cwd and finally the test script is executed.
https://bugzilla.gnome.org/show_bug.cgi?id=793729
We're mostly interested into building and testing everything that gets
pushed to the repository — including merge requests.
When pushing tags, though, we should assume we're spinning a release, so
let's run the dist target, and store the tarball, and the generated
documentation while we're at it, as artifacts on GitLab.
The Dockerfile for the image used for the build is included in tree, and
published on Docker Hub. Using a custom image allows us to avoid the
costly "download and install build dependencies" phase, as well as
controlling the environment a little bit better.
https://bugzilla.gnome.org/show_bug.cgi?id=793635
