silence two build warnings

gant.c: In function ‘chevent’:
gant.c:822:9: warning: variable ‘newdata’ set but not used [-Wunused-but-set-variable]

gant.c:1322:23: warning: unused variable 'opterr' [-Wunused-variable]
   extern int optind, opterr, optopt;
                      ^
gant.c:1322:31: warning: unused variable 'optopt' [-Wunused-variable]
   extern int optind, opterr, optopt;
                              ^
2 warnings generated.