With glib < 2.51.3, gdbus-codegen does not understand "--output-directory" .
Hence, the generated files are like
But gnome.gdbus_codegen() returns a path as if it would be inside
"build/introspection". Hack around that, by patching the correct path
otherwise. This is still ugly, because repeated "ninja -C build" calls
will always try to rebuild this target (because the wrong file name
See also .