Use the optreset variable on BSD systems.

On BSD based operating systems the optreset variable should be used to
reset the internal getopt state. Setting optind to zero is a GNU
extension.

configure.ac

@@ -107,6 +107,9 @@ AC_CHECK_HEADERS([linux/serial.h])
 AC_CHECK_HEADERS([IOKit/serial/ioss.h])
 AC_CHECK_HEADERS([getopt.h])
 
+# Checks for global variable declarations.
+AC_CHECK_DECLS([optreset])
+
 # Checks for library functions.
 AC_FUNC_STRERROR_R
 AC_CHECK_FUNCS([localtime_r gmtime_r])

examples/dctool.c

@@ -217,6 +217,9 @@ main (int argc, char *argv[])
 	argc -= optind;
 	argv += optind;
 	optind = RESET;
+#if defined(HAVE_DECL_OPTRESET) && HAVE_DECL_OPTRESET
+	optreset = 1;
+#endif
 
 	// Translate the help option into a command.
 	char *argv_help[] = {(char *) "help", NULL, NULL};