message: more sensible slack
diff: @@ -84,7 +84,8 @@ impl<'mir, 'tcx> GlobalState {
  // Leave some space to the previous allocation, to give it some chance to be less aligned.
  let slack = {
  let mut rng = memory.extra.rng.as_ref().unwrap().borrow_mut();
  - rng.gen_range(0, align)
  + // This means that `(global_state.next_base_addr + slack) % 16` is uniformly distributed.
  + rng.gen_range(0, 16)
  };
  // From next_base_addr + slack, round up to adjust for alignment.
  let base_addr = Self::align_addr(global_state.next_base_addr + slack, align);
  