Abysmal state of GTK build

[Po Lu]

Users of the GTK 3 build experience many, many problems.  The most
recent such problem is bug#56869, which is definitely a bug in GTK.

Taking into account the very low quality of the GDK X11 backend, which
is not seeing active maintenance, shouldn't the build default to some
other toolkit such as Motif, or even better, no toolkit at all?

Especially considering that a GTK developer (the tail) wants to remove
support for X11 (the dog) in future releases of GTK:

  https://gitlab.gnome.org/GNOME/gtk/-/issues/5004