externals: Update boost to 1.72 and add Boost Context

boost/thread/exceptional_ptr.hpp

@@ -0,0 +1,44 @@
+// 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)
+// (C) Copyright 2014 Vicente J. Botet Escriba
+
+#ifndef BOOST_THREAD_EXCEPTIONAL_PTR_HPP
+#define BOOST_THREAD_EXCEPTIONAL_PTR_HPP
+
+#include <boost/thread/detail/move.hpp>
+#include <boost/exception_ptr.hpp>
+
+#include <boost/config/abi_prefix.hpp>
+
+namespace boost
+{
+  struct exceptional_ptr {
+    exception_ptr ptr_;
+
+    exceptional_ptr() : ptr_() {}
+    explicit exceptional_ptr(exception_ptr ex) : ptr_(ex) {}
+    template <class E>
+    explicit exceptional_ptr(BOOST_FWD_REF(E) ex) : ptr_(boost::copy_exception(boost::forward<E>(ex))) {}
+  };
+
+  template <class E>
+  inline exceptional_ptr make_exceptional(BOOST_FWD_REF(E) ex) {
+    return exceptional_ptr(boost::forward<E>(ex));
+  }
+
+  inline exceptional_ptr make_exceptional(exception_ptr ex)
+  {
+    return exceptional_ptr(ex);
+  }
+
+  inline exceptional_ptr make_exceptional()
+  {
+    return exceptional_ptr();
+  }
+
+} // namespace boost
+
+#include <boost/config/abi_suffix.hpp>
+
+#endif