message: make sure the raw_ptr macros also avoid UB
diff: -#![feature(unsize, coerce_unsized, raw_ref_op)]
  +#![feature(unsize, coerce_unsized, raw_ref_op, raw_ref_macros)]
  use std::collections::hash_map::DefaultHasher;
  use std::hash::Hash;
  +use std::ptr;
  fn test_basic() {
  #[repr(packed)]
  @@ -45,7 +46,9 @@ fn test_basic() {
  assert_eq!({x.b}, 99);
  // but we *can* take a raw pointer!
  assert_eq!(unsafe { (&raw const x.a).read_unaligned() }, 42);
  + assert_eq!(unsafe { ptr::raw_const!(x.a).read_unaligned() }, 42);
  assert_eq!(unsafe { (&raw const x.b).read_unaligned() }, 99);
  + assert_eq!(unsafe { ptr::raw_const!(x.b).read_unaligned() }, 99);
  x.b = 77;
  assert_eq!({x.b}, 77);
  