Every printf()-like function sooner or later needs its vprintf()-like buddy. The next commit will need qobject_from_jsonf_nofail()'s buddy, and qdict_from_jsonf_nofail()'s buddy will be used later in this series. Add both. Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org> Reviewed-by: Eric Blake <eblake@redhat.com> Message-Id: <20180806065344.7103-8-armbru@redhat.com>