build: Use the appropriate NAMESPACE variable everywhere
build: Use the appropriate NAMESPACE variable everywhere

We're inconsistently using the NAMESPACE variable instead of passing
the --identifier-prefix and --symbol-prefix command line arguments to
the introspection scanner.

jigpu/clutter,Distrotech/clutter,jigpu/clutter,GNOME/clutter,jigpu/clutter,Distrotech/clutter,Distrotech/clutter,Distrotech/clutter,GNOME/clutter,GNOME/clutter,jigpu/clutter,GNOME/clutter,Distrotech/clutter,jigpu/clutter,jigpu/clutter,Distrotech/clutter,GNOME/clutter