Fix implicit declaration of functions.
--- configure.orig	1998-11-02 17:33:47.000000000 -0600
+++ configure	2021-04-15 16:24:11.000000000 -0500
@@ -1062,6 +1062,7 @@
 #line 1063 "configure"
 #include "confdefs.h"
 #include <ctype.h>
+#include <stdlib.h>
 #define ISLOWER(c) ('a' <= (c) && (c) <= 'z')
 #define TOUPPER(c) (ISLOWER(c) ? 'A' + ((c) - 'a') : (c))
 #define XOR(e, f) (((e) && !(f)) || (!(e) && (f)))
--- hpwd.c.orig	1998-04-11 03:26:59.000000000 -0500
+++ hpwd.c	2021-04-15 16:30:34.000000000 -0500
@@ -24,6 +24,7 @@
 # endif
 
 # include <stdio.h>
+# include <string.h>
 
 # include "hfs.h"
 # include "hcwd.h"
--- libhfs/configure.orig	1998-11-02 17:33:58.000000000 -0600
+++ libhfs/configure	2021-04-15 16:28:14.000000000 -0500
@@ -1277,6 +1277,8 @@
   cat > conftest.$ac_ext <<EOF
 #line 1279 "configure"
 #include "confdefs.h"
+#include <stdlib.h>
+#include <string.h>
 
 main()
 {