Will Smith will star in “I Am Legend,” the long-gestating Warner Bros. adaptation of the Richard Matheson novel to be directed by “Constantine” helmer Francis Lawrence. “Legend” came closest to getting made back in 1997 with Ridley Scott directing Arnold Schwarzenegger. Warners applied the brakes because the budget hovered around $108 million, a figure considered high at the time. Michael Bay and Smith then aligned to have a go at the film in 2002, but the pairing didn’t advance. Set in post-apocalyptic New York, “Legend” is about the last healthy man following the release of a virus that decimates the population. To survive, he must battle mutants that wreak havoc during the night.