Nearly everything in that module relies on at least some hardcoded compiler magic (what Rust calls "language items", with a `#[lang = "..."]` attribute on the definition). The only exception is `Send`—and even that is still an auto trait, which on stable Rust can only be defined by the standard library. (There are plans to also remove the lang-item status from `Unpin`.)

Fair point, I was only looking at the structs, not the traits.