errtbl.c: In function ‘main’:
errtbl.c:2151:18: warning: ‘optarg’ redeclared without dllimport attribute: previous dllimport
ignored [-Wattributes]
 2151 |     extern char *optarg; /* argv index of the next arg */
      |                  ^~~~~~
errtbl.c:2152:16: warning: ‘optind’ redeclared without dllimport attribute: previous dllimport
ignored [-Wattributes]
 2152 |     extern int optind;   /* argv index of the next arg */
      |                ^~~~~~