Include the generated trace.h the same way as we do everywhere else.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190315145123.28030-3-armbru@redhat.com>
Acked-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>