gtk-builder-tool-validate: Use GtkBuilder to find parent class
This allows LD_PRELOAD
to be used to load an additional libarary, and
therefore it's possible to validate composite templates that subclass a
class that's not part of gtk.
This allows LD_PRELOAD
to be used to load an additional libarary, and
therefore it's possible to validate composite templates that subclass a
class that's not part of gtk.