GNUmifluz: SH_TAILQ_INSERT_HEAD

do { \
 if ((head)->stqh_first != -1) { \
 (elm)->field.stqe_next = \
 (head)->stqh_first - SH_PTR_TO_OFF(head, elm); \
 SH_TAILQ_FIRSTP(head, type)->field.stqe_prev = \
 SH_TAILQ_NEXT_TO_PREV(elm, field); \
 } else { \
 (elm)->field.stqe_next = -1; \
 (head)->stqh_last = \
 SH_PTR_TO_OFF(head, &(elm)->field.stqe_next); \
 } \
 (head)->stqh_first = SH_PTR_TO_OFF(head, elm); \
 (elm)->field.stqe_prev = \
 SH_PTR_TO_OFF(elm, &(head)->stqh_first); \
} while (0)