Update config.{guess,sub}

...to latest versions from <http://git.savannah.gnu.org/gitweb/?p=config.git;
a=blob_plain;f=config.guess;hb=HEAD> and <http://git.savannah.gnu.org/gitweb/?
p=config.git;a=blob_plain;f=config.sub;hb=HEAD>

but retain...

commit 25a09c87
Date:   Wed Jun 7 12:23:17 2017 +0200

    iOS, add support for arm64

    Added general support for arm64
    Removed experimental/prototype from normal build

Change-Id: Ic36a9fb9d20344ff0ddc6b293ed3bd48cf140a31
Reviewed-on: https://gerrit.libreoffice.org/72200
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>