meson: Fix usage of glib as a subproject dependency

We include glib headers, so we need to ensure that we also pull in the glib dependency correctly, to inherit the right include flags. Also doesn't lead to overlinking because meson uses --as-needed by default.

This wasn't noticed earlier because when building against glib inside a prefix, glib and gobject headers are in the same location.

This is needed to build gtk+ and all dependencies from scratch on Windows with meson subprojects. See also: gdk-pixbuf!25