Fix:

error: implicitly declaring library function 'exit' with type 'void (int) __attribute__((noreturn))' [-Werror,-Wimplicit-function-declaration]
--- asc85ec.c.orig	2002-02-04 05:39:21.000000000 -0600
+++ asc85ec.c	2020-12-07 02:02:30.000000000 -0600
@@ -2,6 +2,7 @@
 /* (C) Thomas Merz 1994-2002 */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <fcntl.h>
 
 /* try to identify Mac compilers */