make clang happier about unused argc/argv in main()

threads.c

@@ -21,7 +21,7 @@ void dienomem() {
   exit(1);
 }
 
-int main(int argc, char *argv[]) {
+int main(void) {
   pthread_t threads[NUM_THREADS];
 
   for (int t = 0; t < NUM_THREADS; t++) {