Implement C++1y decltype(auto).

llvm-svn: 180610
diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
index 00ca3d8..dff3b64 100644
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -942,6 +942,7 @@
 /// [GNU]     '_Complex'
 /// [C++11]   'auto'
 /// [C++11]   'decltype' ( expression )
+/// [C++1y]   'decltype' ( 'auto' )
 ///
 ///         type-name:
 ///           class-name