6690928: Use spinning in combination with yields for workstealing termination

Substitute a spin loop for most calls to yield() to reduce the stress on the system.

Reviewed-by: tonyp

hotspot/src/share/vm/gc_implementation/parallelScavenge/psScavenge.cpp

@@ -615,6 +615,10 @@ bool PSScavenge::invoke_no_policy() {
     gc_task_manager()->print_task_time_stamps();
   }
 
+#ifdef TRACESPINNING
+  ParallelTaskTerminator::print_termination_counts();
+#endif
+
   return !promotion_failure_occurred;
 }