Fix build.

Build broken due to a rare lock checking violation happening during
oat generation. Added a new lock level for the mark stack lock since
it may be acquired with the globals/pins lock.

Change-Id: I944ae0700c66ad050fe3d23aba2f2c377c5df799
diff --git a/runtime/gc/collector/mark_sweep.h b/runtime/gc/collector/mark_sweep.h
index d5f4042..fdd0c86 100644
--- a/runtime/gc/collector/mark_sweep.h
+++ b/runtime/gc/collector/mark_sweep.h
@@ -446,7 +446,7 @@
 
   UniquePtr<Barrier> gc_barrier_;
   Mutex large_object_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
-  Mutex mark_stack_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
+  Mutex mark_stack_lock_ ACQUIRED_AFTER(Locks::classlinker_classes_lock_);
 
   const bool is_concurrent_;