After a fall in the first qualifying round, the most successful halfpipe rider in history rose to the occasion Wednesday and pulled off a do-or-die run—and now Shaun White is in the medal round at his fifth and final Olympics. “I can’t tell you the relief I felt off that last hit,” White said. “It was just the thrill and excitement to be going to finals.” White, 35, earned the finals trip after he eased up on “The Tomahawk”—a trick he invented more than a decade ago that includes a frontside takeoff and 1260-degree diagonal, off-axis angle. “I was thinking a lot about that, like, how if the ne…