Under the scalding hot sun of the Brazilian northeast, a group of young boys kicks dirt up while running over a football. All but one, Gugu, whose energy is directed elsewhere: a pompous dance number by the sidelines of the improvised field. Allan Deberton’s “Gugu’s World,” world premiering at the Berlin Film Festival , follows the titular boy to build a poignant look at the difficulties of childhood for those who don’t quite fit in.  The tender drama enlists some heavyweights alongside