message: fix accessing fields other than the first in packed structs
diff: @@ -208,12 +208,13 @@ impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  _ => bug!("field access on non-product type: {:?}", base_layout),
  };
  + let ptr = base_ptr.offset(offset.bytes());
  +
  if packed {
  let size = self.type_size(field_ty)?.expect("packed struct must be sized");
  - self.memory.mark_packed(base_ptr, size);
  + self.memory.mark_packed(ptr, size);
  }
  - let ptr = base_ptr.offset(offset.bytes());
  let extra = if self.type_is_sized(field_ty) {
  LvalueExtra::None
  } else {
  