It’s not a Texas chainsaw massacre, but the spirit of Tobe Hooper’s original scuzz-slasher classic looms large over “X,” writer-director Ti West’s tribute to ’70s cinema, porn, horror and godlessness on the Texas plains. It’s 1979 and a group of youngsters heads out to a rented cabin to shoot an adult film when they run afoul with the landowners and start getting picked off one by one. Th premise isn’t going to set the world on fire. But West (“The House of the Devil”) is a student of the genre, and he crafts a loving ode to both the soul and sensibilities of his ’70s heroes, and elevates the …