Big cleanup of packages not built for all arches
    
    This adds correct arch= tags for all non-optional packages which
    currently don't have one, but aren't built for all arches, using
    the output from `check-missing`.
    
    I think it's fine to have no arch= tag on optional packages,
    because they're by definition optional. It's okay for an optional
    thing to be missing.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>