externals: Update boost to 1.72 and add Boost Context

boost/smart_ptr/detail/sp_forward.hpp

@@ -0,0 +1,52 @@
+#ifndef BOOST_SMART_PTR_DETAIL_SP_FORWARD_HPP_INCLUDED
+#define BOOST_SMART_PTR_DETAIL_SP_FORWARD_HPP_INCLUDED
+
+// MS compatible compilers support #pragma once
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1020)
+# pragma once
+#endif
+
+//  detail/sp_forward.hpp
+//
+//  Copyright 2008,2012 Peter Dimov
+//
+//  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
+
+#include <boost/config.hpp>
+
+namespace boost
+{
+
+namespace detail
+{
+
+#if !defined( BOOST_NO_CXX11_RVALUE_REFERENCES )
+
+#if defined( BOOST_GCC ) && __GNUC__ * 100 + __GNUC_MINOR__ <= 404
+
+// GCC 4.4 supports an outdated version of rvalue references and creates a copy of the forwarded object.
+// This results in warnings 'returning reference to temporary'. Therefore we use a special version similar to std::forward.
+template< class T > T&& sp_forward( T && t ) BOOST_NOEXCEPT
+{
+    return t;
+}
+
+#else
+
+template< class T > T&& sp_forward( T & t ) BOOST_NOEXCEPT
+{
+    return static_cast< T&& >( t );
+}
+
+#endif
+
+#endif
+
+} // namespace detail
+
+} // namespace boost
+
+#endif  // #ifndef BOOST_SMART_PTR_DETAIL_SP_FORWARD_HPP_INCLUDED