By only showing the g-ir-scanner void typedefs it will make it print warnings. Lets please it by showing the actual typedef. https://bugzilla.gnome.org/show_bug.cgi?id=768977
If we want to put a cogl winsys backend in mutter, that backend need to have access to the internal workings of cogl. https://bugzilla.gnome.org/show_bug.cgi?id=768976