Instead of using str_fmt this method should just print a space num_spaces times:

  // returns a format string to print a julong with the given width. E.g,
  // printf(num_fmt(6), julong(10)) would print out the number 10 with 4
  // leading spaces.
PRAGMA_DIAG_PUSH
PRAGMA_FORMAT_NONLITERAL_IGNORED

  static void print_julong(outputStream* st, int width, julong n) {
    int num_spaces = width - julong_width(n);
    if (num_spaces > 0) {
      st->print(str_fmt(num_spaces), "");
    }
    st->print(JULONG_FORMAT, n);
  }
PRAGMA_DIAG_POP