Missing includes for FreeBSD.

Change-Id: I4ea02a41ed614047ecda156d0c572b04baa174e6
Reviewed-on: https://boringssl-review.googlesource.com/1852
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/tool/args.cc b/tool/args.cc
index 1882de0..6cbfab6 100644
--- a/tool/args.cc
+++ b/tool/args.cc
@@ -16,6 +16,7 @@
 #include <vector>
 #include <map>
 
+#include <stdio.h>
 #include <string.h>
 
 #include "internal.h"