Convert the task->flags to atomic_uint_fast32_t

The isc_task_t flags have been converted to atomic_uint_fast32_t and the
atomic_fetch_or and atomic_fetch_and are used to set and clear flags.
77 jobs for !2358 with 1119-tsan-lib/isc/task.c in 38 minutes and 11 seconds (queued for 7 minutes and 27 seconds)
merge request