This PR was rather meant to get Travis CI working again quickly instead of revamping the way we build for CI.
@kugel- : Do you have already any idea how to get the necessary MSYS2 packages on a Linux host? We would find a way to "port" the `gtk-bundle-from-msys2.sh` to Linux I guess and the hard part is probably substituting `pacman`.
@b4n do mean handling with "extra workload" serving the bundle downloads to Travis? Or rather replacing Travis and perform the CI builds on our servers? If the former, that's easy. If the latter, I'd rather use a separate VM for that but it won't be a problem.