get lambda example compiling on clang

example/lambda.cpp

@@ -0,0 +1,17 @@
+//[ Lambda
+///////////////////////////////////////////////////////////////////////////////
+// Copyright 2008 Eric Niebler. Distributed under the Boost
+// Software License, Version 1.0. (See accompanying file
+// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// This example builds a simple but functional lambda library using Proto.
+
+#include <iostream>
+#include "./lambda.hpp"
+
+int main()
+{
+    using namespace boost::lambda;
+    int i = (_1 + _1)(42);
+    std::cout << i << std::endl;
+}