This blocks the removal/defaulting of ShenandoahSuspendibleWorkers. It is currently set at "false", and normal heuristics enables it to "true". Traversal GC code handles it half-heartedly, with having ShenandoahSuspendibleThreadSetJoiner scopes at interesting places, but defining the actual yields as:

bool ShenandoahTraversalGC::check_and_handle_cancelled_gc(TaskTerminator* terminator, bool sts_yield) {
  if (_heap->cancelled_gc()) {
    return true;
  }
  return false;
}

This was found by static analyzers that complained both arguments are unused.