gather: Don't pull multiple debuginfo packages
    
    When there is a noarch subpackage, all compatible debuginfo would be
    pulled in, which is not desirable.
    
    Example: Server.x86_64 needs pkg.x86_64 and pkg-data.noarch. We only
    want pkg-debuginfo.x86_64, but without this patch even
    pkg-debuginfo.i686 would get in.
    
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>