`__BYTE_ORDER` is required for v8 to compile ([v8/src/objects.h#5883-5889](https://github.com/v8/v8/blob/master/src/objects.h#L5883-L5889)). After a discussion with @TooTallNate and @bnoordhuis on irc, we're going to assume it's safe to use. And since it's already required there's less duplication of code.