Fix some GCC 15 problems.

--- ace-1.4/lib/imagelib.c	2012-03-24 18:00:49.000000000 +0000
+++ ace-1.4/lib/imagelib.c	2025-07-04 18:13:31.651655712 +0100
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 #include "imagelib.h"
 #include "cards.h"
--- ace-1.4/lib/make-imglib.c	2025-07-04 18:14:43.138967980 +0100
+++ ace-1.4/lib/make-imglib.c	2025-07-04 18:12:56.829669718 +0100
@@ -5,6 +5,7 @@
 #include <sys/stat.h>
 #include <unistd.h>
 #include <dirent.h>
+#include <ctype.h>
 
 #include <png.h>
 
@@ -202,7 +203,7 @@
   char *rv;
   if (string) {
     next = string;
-    return;
+    return 0;
   }
   while (*next && !isgraph(*next)) next++;
   if (!*next) return 0;
@@ -257,7 +258,7 @@
     case 'd':
       depfile = fopen(optarg, "w");
       if (!depfile) {
-	fprintf(stderr, "Unable to open dependency file %s for writing\n", depfile);
+	fprintf(stderr, "Unable to open dependency file %s for writing\n", optarg);
 	perror("The error was");
 	exit(1);
       }