extras: pthread: fix check for C mode with paranoid -Werror=old-style-declaration and -Werror=unused-variable

waflib/extras/pthread.py

@@ -9,13 +9,17 @@ PTHREAD_CHECK = '''
 #include <pthread.h>
 
 static void* fun(void* params) {
+    (void)params;
     return NULL;
 }
 
-int main() {
+int main(int argc, char **argv) {
     pthread_t thread;
+    (void)argc;
+    (void)argv;
     pthread_create(&thread, NULL, &fun, NULL);
     pthread_join(thread, NULL);
+    return 0;
 }
 '''