PR libgomp/51376
PR libgomp/56073
* task.c (GOMP_task): Revert 2011-12-09 change.
(GOMP_taskwait): Likewise. Instead use atomic load with acquire
barrier to read task->children..
(gomp_barrier_handle_tasks): ..and matching atomic store with
release barrier here when setting parent->children to NULL.
From-SVN: r195370
