Add __arraycount() macro from NetBSD
diff --git a/include/bsd/sys/cdefs.h b/include/bsd/sys/cdefs.h
index d1cc419..98333d1 100644
--- a/include/bsd/sys/cdefs.h
+++ b/include/bsd/sys/cdefs.h
@@ -156,6 +156,12 @@
#endif
/*
+ * Return the number of elements in a statically-allocated array,
+ * __x.
+ */
+#define __arraycount(__x) (sizeof(__x) / sizeof(__x[0]))
+
+/*
* We define this here since <stddef.h>, <sys/queue.h>, and <sys/types.h>
* require it.
*/