Cannes Film Festival stars a 76-year old action star and is a reboot of a movie that first dazzled moviegoers in 1993. That’s a time, in case you forgot, before TikTok or smartphones, Facebook or Amazon, or any number of technological changes that have reshaped our world and the movie business along with them. And yet, “Cliffhanger,” with Sylvester Stallone bravely summiting the mountain again, is seen as one of the most commercial scripts out there for buyers hoping to make an adventure film that can traverse borders and bring crowds. With a nod to the younger audiences who will be needed to turn up if the movie is going to replicate the original’s blockbuster status, the producers teased that casting is currently underway for a (presumably younger?) actor to share the screen with Sly. But who will that be?