Update clang to r339409b.

Change-Id: Ied8a188bb072c40035320acedc86164b66d920af
diff --git a/linux-x64/clang/include/llvm/ADT/DenseSet.h b/linux-x64/clang/include/llvm/ADT/DenseSet.h
index b495e25..52fe4ad 100644
--- a/linux-x64/clang/include/llvm/ADT/DenseSet.h
+++ b/linux-x64/clang/include/llvm/ADT/DenseSet.h
@@ -136,8 +136,8 @@
   public:
     using difference_type = typename MapTy::const_iterator::difference_type;
     using value_type = ValueT;
-    using pointer = value_type *;
-    using reference = value_type &;
+    using pointer = const value_type *;
+    using reference = const value_type &;
     using iterator_category = std::forward_iterator_tag;
 
     ConstIterator() = default;