CIRCQ_FIRST
#define CIRCQ_EMPTY(elem) (CIRCQ_FIRST(elem) == (elem))
for ((elem) = CIRCQ_FIRST(list); \
(elem) = CIRCQ_FIRST(elem))
first_new = timeout_from_circq(CIRCQ_FIRST(&timeout_new));
to = timeout_from_circq(CIRCQ_FIRST(&timeout_todo));
to = timeout_from_circq(CIRCQ_FIRST(todo));
p = CIRCQ_FIRST(&timeout_wheel[b]);
p = CIRCQ_FIRST(p);