GNUmifluz: CIRCLEQ_INSERT_HEAD

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