Extract is_error_code_enum, is_error_condition_enum into their own headers

test/is_error_condition_enum_test.cpp

@@ -0,0 +1,40 @@
+// Copyright 2020 Peter Dimov.
+// Distributed under the Boost Software License, Version 1.0.
+// http://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/system/is_error_condition_enum.hpp>
+#include <boost/core/lightweight_test.hpp>
+
+enum condition
+{
+    c1 = 1,
+    c2,
+    c3
+};
+
+namespace boost
+{
+namespace system
+{
+
+template<> struct is_error_condition_enum< ::condition >
+{
+    static const bool value = true;
+};
+
+}
+}
+
+boost::system::error_condition make_error_condition( ::condition e );
+
+enum not_condition
+{
+};
+
+int main()
+{
+    BOOST_TEST( boost::system::is_error_condition_enum< ::condition >::value );
+    BOOST_TEST( !boost::system::is_error_condition_enum< ::not_condition >::value );
+
+    return boost::report_errors();
+}