private static void printUsage(PrintStream out) {
        out.println("Usage: java -Dconfig.dest=<dir> -Dconfig.spec=<path> [-Dconfig.lang=cpp -Dconfig.subdir=<dir>] [-Dconfig.dumpTree=true] MakeConfig");
        out.println("       (default language for generated code is Java)");
    }
Generates the code and print it to this.out.
configgen/src/main/java/com/yahoo/config/codegen/MakeConfig.java