externals: Update boost to 1.72 and add Boost Context

libs/system/build/Jamfile.v2

@@ -0,0 +1,25 @@
+# Boost System Library Build Jamfile
+
+# (C) Copyright Beman Dawes 2002, 2006
+
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or www.boost.org/LICENSE_1_0.txt)
+
+# See library home page at http://www.boost.org/libs/system
+
+project boost/system
+    : source-location ../src
+    : usage-requirements  # pass these requirement to dependents (i.e. users)
+      <link>shared:<define>BOOST_SYSTEM_DYN_LINK=1
+      <link>static:<define>BOOST_SYSTEM_STATIC_LINK=1
+    ;
+
+SOURCES = error_code ;
+
+lib boost_system
+   : $(SOURCES).cpp
+   : <link>shared:<define>BOOST_SYSTEM_DYN_LINK=1
+     <link>static:<define>BOOST_SYSTEM_STATIC_LINK=1
+   ;
+
+boost-install boost_system ;

libs/system/src/error_code.cpp

@@ -0,0 +1,31 @@
+//  error_code stub implementation, for compatibility only
+
+//  Copyright Beman Dawes 2002, 2006
+//  Copyright Peter Dimov 2018
+
+//  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)
+
+//  See library home page at http://www.boost.org/libs/system
+
+//----------------------------------------------------------------------------//
+
+// define BOOST_SYSTEM_SOURCE so that <boost/system/config.hpp> knows
+// the library is being built (possibly exporting rather than importing code)
+#define BOOST_SYSTEM_SOURCE
+
+#include <boost/system/config.hpp>
+
+namespace boost
+{
+
+namespace system
+{
+
+BOOST_SYSTEM_DECL void dummy_exported_function()
+{
+}
+
+} // namespace system
+
+} // namespace boost