The fourth floor of the Museum of Contemporary Art Chicago, through Oct. 1, will be a haunted house, a liminal space, a gateway to a past not settled. That’s one way to describe “Public Enemy,” a sweeping new survey of four decades of absorbing work by Gary Simmons, whose name alone, first heard in the late 1980s, conjures the ghosts of the art world’s past. Indeed, the show itself, with its .