Advancing their causes at the Writers Guild of America Awards Saturday, the writers of winners “The Big Short” (Adapted Screenplay) and “Spotlight” (Original Screenplay) reminded attendees that their movies were about serious subjects. Screenwriter Josh Singer thanked Boston Globe reporter Ellen McNamara and survivor Phil Saviano, who were in the Hyatt Regency Century Plaza ballroom (writer-director Tom McCarthy accepted in New York at an earlier ceremony).