Driver
------

if valid program (syntactically and semantically)
  // Write Assembly
  outFile.open (fileNameBase + ".s");
  CodeGeneratorVisitor cgv (outFile);
  root->accept (&cgv);
  outFile.close ();

  cout << "Writing executable to \"" << fileNameBase << "\"\n";
  string gccCall = "gcc -m32 -g "
                    + fileNameBase + ".s -o " + fileNameBase;
  int result = system (gccCall.c_str ());

  if (result == -1)
    cout << "Error occurred while attempting to build executable!\n";
  else
    cout << "Success!\n";