// So, when we thaw a MUT_ARR_PTRS_FROZEN, we must cope with two cases:
// either it is on a mut_list, or it isn't. We adopt the convention that
// the mut_link field is NULL if it isn't on a mut_list, and the GC
// maintains this invariant.
//
// So, when we thaw a MUT_ARR_PTRS_FROZEN, we must cope with two cases:
// either it is on a mut_list, or it isn't. We adopt the convention that
// the mut_link field is NULL if it isn't on a mut_list, and the GC
// maintains this invariant.
//