With meson >= 47.0, building gnome-shell will fail when --rebuild-types is used as an option for gtk-doc, so stop using that option and bump the meson requirement. https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/191
Meson is on track to replace autotools as the build system of choice, so support it in addition to autotools. If all goes well, we'll eventually be able to drop the latter ... https://bugzilla.gnome.org/show_bug.cgi?id=783229