openmp: Notify team barrier of pending tasks in omp_fulfill_event

The team barrier should be notified of any new tasks that become runnable
as the result of a completing task, otherwise the barrier threads might
not resume processing available tasks, resulting in a hang.

2021-05-17  Kwok Cheung Yeung  <kcy@codesourcery.com>

	libgomp/
	* task.c (omp_fulfill_event): Call gomp_team_barrier_set_task_pending
	if new tasks generated.
	* testsuite/libgomp.c-c++-common/task-detach-13.c: New.