GNUmifluz: CIRCLEQ_INSERT_TAIL

do { \
 (elm)->field.cqe_next = (void *)(head); \
 (elm)->field.cqe_prev = (head)->cqh_last; \
 if ((head)->cqh_first == (void *)(head)) \
 (head)->cqh_first = (elm); \
 else \
 (head)->cqh_last->field.cqe_next = (elm); \
 (head)->cqh_last = (elm); \
} while (0)