Fix ta_wakes_up_on_or_before

[peterharperuk]

Handle target in the past and running for > 2^32 us.

Fixes #2186

[kilograham]

Hmm; i think the bug lies elsewhere...

does this help?

static inline bool ta_wakes_up_on_or_before(alarm_pool_timer_t *timer, uint alarm_num, int64_t target) {
    int64_t current = (int64_t)timer_time_us_64(timer_hw_from_timer(timer));
    int64_t time_til_target = target - current;
    uint32_t time_til_alarm = timer_hw_from_timer(timer)->alarm[alarm_num] - (uint32_t)current;
    return time_til_alarm <= time_til_target;
}

(it also should fix another fairly glaring error if you'd been running for > 2^32 us

[peterharperuk]

@kilograham Your fix seems to work. I think my analysis was wrong? It was actually seems stuck on WFE? I'll use your fix instead.