Clutter had support for internal children in its early revisions, but they
were deprecated for long time (commit f41061b8df, more than 7 years ago) and
no one is using them in both clutter and in gnome-shell.
So remove any alternative code path that uses internal children.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/816
Some of the marshallers we generate in `clutter-marshal.list` are also
available in GLib, so we don't need to generate them ourselves. Even
more, by passing NULL to `g_signal_new` in these cases will actually
internally optimize this even more by also setting the valist
marshaller, which is a little bit faster than the regular marshalling
using `GValue` and libffi.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/700
In cogl use cogl-config.h and in clutter use clutter-build-config.h. We
can't use clutter-config.h in clutter because its already used and
installed.
https://bugzilla.gnome.org/show_bug.cgi?id=768976
