Eddie Izzard, who’s in town to film a Gus Van Sant-directed HBO pilot about the Salem witch trials (which, for now, is being called “The Devil You Know”) got support from friends during his performance at the American Repertory Theater in Cambridge on Saturday night. In the audience for his one-night-only, sold-out show were Van Sant, show writer Jenji Kohan, and “Devil” actors Damien Molony, Ever Carradine, Mia Barron, Ismenia Mendes, and Matthew James Thomas, who also starred in the ART’s production of “Pippin.” “Cheering on Papa Putnam tonight,” tweeted Molony, who plays Robert Putnam, son of the Izzard character, on the show.