qapi: Document shortcoming with union 'data' branch Add a FIXME to remind us to fully audit whether removing the 'void *data' branch of each qapi union type can be done safely. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <1438297637-26789-1-git-send-email-eblake@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>