$NetBSD$

Include missing header.

--- src/defaults.cxx.orig	2024-10-25 23:21:16.000000000 +0000
+++ src/defaults.cxx
@@ -1,5 +1,6 @@
 #include <libintl.h>
 #include <math.h>
+#include <stdlib.h>
 #include "defaults.h"
 #include "string.h"