message: use mutable reference
diff: @@ -74,7 +74,7 @@ fn vec_reallocate() -> Vec<u8> {
  fn vec_push_ptr_stable() {
  let mut v = Vec::with_capacity(10);
  v.push(0);
  - let v0 = unsafe { &*(&v[0] as *const _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
  + let v0 = unsafe { &mut *(&mut v[0] as *mut _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
  v.push(1);
  let _val = *v0;
  }
  @@ -82,7 +82,7 @@ fn vec_push_ptr_stable() {
  fn vec_extend_ptr_stable() {
  let mut v = Vec::with_capacity(10);
  v.push(0);
  - let v0 = unsafe { &*(&v[0] as *const _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
  + let v0 = unsafe { &mut *(&mut v[0] as *mut _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
  // `slice::Iter` (with `T: Copy`) specialization
  v.extend(&[1]);
  let _val = *v0;
  @@ -99,7 +99,7 @@ fn vec_extend_ptr_stable() {
  fn vec_truncate_ptr_stable() {
  let mut v = vec![0; 10];
  - let v0 = unsafe { &*(&v[0] as *const _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
  + let v0 = unsafe { &mut *(&mut v[0] as *mut _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
  v.truncate(5);
  let _val = *v0;
  }
  