message: test the Rc::{into,from}_raw roundtrip
  This uses some pointer arithmetic based on field offsets
diff: @@ -8,6 +8,16 @@ fn rc_refcell() -> i32 {
  x
  }
  +fn rc_raw() {
  + let r = Rc::new(0);
  + let r2 = Rc::into_raw(r.clone());
  + let r2 = unsafe { Rc::from_raw(r2) };
  + assert!(Rc::ptr_eq(&r, &r2));
  + drop(r);
  + assert!(Rc::try_unwrap(r2).is_ok());
  +}
  +
  fn main() {
  rc_refcell();
  + rc_raw();
  }
  