In “Terminator Genisys,” which I guess must be described (God help us) as an “alternate-universe reboot” of the sci-fi action franchise launched by James Cameron 31 years ago, some digital wizardry is wrought so that we see Arnold Schwarzenegger’s eponymous cyborg land in Los Angeles in 1984. He looks approximately like the old (i.e., young) Ahh-nold, and not so much like the leather-jacketed antihero of Cameron’s first film as the bulging, sleek, poofily coiffed bodybuilder of “Stay Hungry” and “Pumping Iron.” Or rather, he looks like a model of the young Arnold sculpted in plasticine and brought to life, which serves as a decent analogy for this entire movie, a confusing and expensive jumble of recycled parts.It’s hard to say whether that spectral visitation from a lost pop-culture icon is more wistful or more creepy, especially set against the wizened, weatherbeaten and visibly smaller Schwarzenegger we see later in the film.