ldapupdate: Add support for Debian multiarch
    
    And since Fedora 28 dropped support for non-64bit, hardcode default LIBARCH as 64.
    
    Fixes: https://pagure.io/freeipa/issue/7555
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>