meson: Allow to build as a static library
This is requested by the GNOME Settings maintainer.
This has bee cargo culted from https://gitlab.gnome.org/GNOME/libgd/blob/master/libgd/meson.build.
This is requested by the GNOME Settings maintainer.
This has bee cargo culted from https://gitlab.gnome.org/GNOME/libgd/blob/master/libgd/meson.build.