SgmlFOTBuilder cxx 396 20 warning format expects argument of type int

SgmlFOTBuilder.cxx:396:20: warning: format ‘%d’ expects argument of type ‘int’, but argument 3 has type ‘long int’ [-Wformat=]
  396 |   sprintf(buf, "%03d", u.n);
      |                 ~~~^   ~~~
      |                    |     |
      |                    int   long int
      |                 %03ld