CHICAGO — A gas giveaway by entrepreneur and former mayoral candidate Willie Wilson caused a headache for some Chicagoans Thursday morning, and not from fuel fumes: Cars reportedly lined up overnight in anticipation of the 7 a.m. start time, causing backups near the preselected gas stations around the city. Commenters on Wilson’s Facebook page complained of lines of cars stretching for blocks. “I’m burning gas trying to get gas,” one user wrote. Wilson pledged to give away $200,000 of gasoline via $50 gifts to motorists filling up Thursday, on a first-come, first-serve basis. But from social m…