Make error_code, error_condition literal if C++14 constexpr is available

test/Jamfile.v2

@@ -142,6 +142,12 @@ project
          [ run before_main_test.cpp
            :  :  : -<library>/boost/system//boost_system <define>BOOST_ERROR_CODE_HEADER_ONLY : before_main_test_header
          ]
+         [ run constexpr_test.cpp
+           :  :  : <link>static : constexpr_test_static
+         ]
+         [ run constexpr_test.cpp
+           :  :  : <link>shared : constexpr_test_shared
+         ]
          ;
 
 # Quick (CI) test

test/constexpr_test.cpp

@@ -0,0 +1,40 @@
+
+// Copyright 2018 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+
+#include <boost/system/error_code.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/static_assert.hpp>
+
+#if !defined(BOOST_SYSTEM_HAS_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Skipping constexpr test, BOOST_SYSTEM_HAS_CONSTEXPR isn't defined")
+int main() {}
+
+#else
+
+using namespace boost::system;
+
+constexpr error_code e1( 1, system_category() );
+
+BOOST_STATIC_ASSERT( e1.value() == 1 );
+BOOST_STATIC_ASSERT( e1.category() == system_category() );
+
+constexpr error_code e2( 2, generic_category() );
+
+BOOST_STATIC_ASSERT( e2.value() == 2 );
+BOOST_STATIC_ASSERT( e2.category() == generic_category() );
+
+int main()
+{
+    error_code e1_( 1, system_category() );
+    BOOST_TEST_EQ( e1, e1_ );
+
+    error_code e2_( 2, generic_category() );
+    BOOST_TEST_EQ( e2, e2_ );
+
+    return boost::report_errors();
+}
+
+#endif