“Man of Steel” Henry Cavill is getting raves as the new Clark Kent — but behind the scenes, he had to practice the power of serious bladder control. The hunky star told us at an Alice Tully Hall premiere that his Superman suit fit like an “alien body glove,” which made trips to the men’s room challenging. “It’s quite a tight suit,” he candidly said. “Going to the lavatory wasn’t the easiest thing. It would take some time to get in and out, [so] I’d have to wait. [While filming] in Chicago, I could drink as much as I wanted because I’d sweat, and it would be fine. But [in] Vancouver, where it was cold . . . I got one bottle of water every half-day . . . brutal.” Also at the premiere: Laurence Fishburne, Amy Adams and Kevin Costner.