message: add write_bytes() test for a larger-than-u128 struct
diff: +#[repr(C)]
  +#[derive(Copy, Clone)]
  +struct Foo {
  + a: u64,
  + b: u64,
  + c: u64,
  +}
  +
  fn main() {
  const LENGTH: usize = 10;
  let mut v: [u64; LENGTH] = [0; LENGTH];
  @@ -14,4 +22,24 @@ fn main() {
  for idx in 0..LENGTH {
  assert_eq!(v[idx], 0xabababababababab);
  }
  +
  + // -----
  +
  + let mut w: [Foo; LENGTH] = [Foo { a: 0, b: 0, c: 0 }; LENGTH];
  + for idx in 0..LENGTH {
  + assert_eq!(w[idx].a, 0);
  + assert_eq!(w[idx].b, 0);
  + assert_eq!(w[idx].c, 0);
  + }
  +
  + unsafe {
  + let p = w.as_mut_ptr();
  + ::std::ptr::write_bytes(p, 0xcd, LENGTH);
  + }
  +
  + for idx in 0..LENGTH {
  + assert_eq!(w[idx].a, 0xcdcdcdcdcdcdcdcd);
  + assert_eq!(w[idx].b, 0xcdcdcdcdcdcdcdcd);
  + assert_eq!(w[idx].c, 0xcdcdcdcdcdcdcdcd);
  + }
  }
  