Every so often a songwriter emerges who captures something about the city he calls home. Elliot Smith was as Portland as fixies and strollers. There is something free and unmistakably flyover about Omaha, Nebraska’s Conor Oberst. Kurt Vile — who finished a tour to support his latest record (and first release on Matador Records), Childish Prodigy, at the Black Cat on Thursday — is making his claim as a lo-fi laureate of Philadelphia. Mr. Vile…