message: add padding to immediates
diff: @@ -320,6 +320,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
  immty_from_uint_checked(0u128, uid_t_layout)?, // st_uid
  immty_from_uint_checked(0u128, gid_t_layout)?, // st_gid
  immty_from_uint_checked(0u128, dev_t_layout)?, // st_rdev
  + immty_from_uint_checked(0u128, dev_t_layout)?, // padding
  immty_from_uint_checked(access_sec, time_t_layout)?, // st_atime
  immty_from_uint_checked(access_nsec, long_layout)?, // st_atime_nsec
  immty_from_uint_checked(modified_sec, time_t_layout)?, // st_mtime
  