GNUmifluz: SH_CIRCLEQ_INSERT_TAIL

do { \
 (elm)->field.scqe_next = SH_PTR_TO_OFF(elm, head); \
 (elm)->field.scqe_prev = (head)->scqh_last + \
 (elm)->field.scqe_next; \
 if ((head)->scqh_first == 0) \
 (head)->scqh_first = -(elm)->field.scqe_next; \
 else \
 SH_CIRCLEQ_LASTP(head, type)->field.scqe_next = \
 SH_PTR_TO_OFF(SH_CIRCLEQ_LASTP(head, type), elm); \
 (head)->scqh_last = -(elm)->field.scqe_next; \
} while (0)