Fix a few 4.8 extra anal warnings

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/stat.c b/stat.c
index 245197a..66bea0a 100644
--- a/stat.c
+++ b/stat.c
@@ -1345,7 +1345,7 @@
 	free(threadstats);
 }
 
-static void *__show_running_run_stats(void *arg)
+static void *__show_running_run_stats(void fio_unused *arg)
 {
 	struct thread_data *td;
 	unsigned long long *rt;