ART: Enable more Clang warnings

Change-Id: Ie6aba02f4223b1de02530e1515c63505f37e184c
diff --git a/runtime/gc/collector/concurrent_copying.cc b/runtime/gc/collector/concurrent_copying.cc
index 56919bd..8aa1b52 100644
--- a/runtime/gc/collector/concurrent_copying.cc
+++ b/runtime/gc/collector/concurrent_copying.cc
@@ -804,6 +804,9 @@
  public:
   explicit ConcurrentCopyingClearBlackPtrsVisitor(ConcurrentCopying* cc)
       : collector_(cc) {}
+#ifndef USE_BAKER_OR_BROOKS_READ_BARRIER
+  NO_RETURN
+#endif
   void operator()(mirror::Object* obj) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_)
       SHARED_LOCKS_REQUIRED(Locks::heap_bitmap_lock_) {
     DCHECK(obj != nullptr);