ENH: do not undef cmakedefine stuff, just comment out the line

Source/cmConfigureFileCommand.cxx

@@ -152,14 +152,15 @@ void cmConfigureFileCommand::ConfigureFile()
             {
             cmSystemTools::ReplaceString(inLine,
                                          "#cmakedefine", "#define");
+            fout << inLine << "\n";
             }
           else
             {
             cmSystemTools::ReplaceString(inLine,
                                          "#cmakedefine", "#undef");
+            fout << "/* " << inLine << " */\n";
             }
           }
-        fout << inLine << "\n";
         }
       }
     // close the files before attempting to copy