output "SET RETURN VALUE" when displaying goto programs

To avoid the impression that the 'set return value' instruction alters
control flow, output "SET RETURN VALUE" instead of "RETURN" when displaying
goto programs.

Author: kroening

src/goto-programs/goto_program.cpp

@@ -133,7 +133,7 @@ std::ostream &goto_programt::output_instruction(
     break;
 
   case SET_RETURN_VALUE:
-    out << "RETURN " << format(instruction.return_value()) << '\n';
+    out << "SET RETURN VALUE " << format(instruction.return_value()) << '\n';
     break;
 
   case DECL: