Fix for C23 compatibility.

--- netpbm-10.86.47/buildtools/libopt.c	2023-06-28 18:21:21.000000000 +0100
+++ netpbm-10.86.47/buildtools/libopt.c	2025-07-11 18:16:18.825546633 +0100
@@ -88,13 +88,13 @@
 #include <string.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <stdbool.h>
 
-typedef unsigned char bool;
 #ifndef TRUE
-#define TRUE (1)
+#define TRUE true
 #endif
 #ifndef FALSE
-#define FALSE (0)
+#define FALSE false
 #endif
 
 #ifdef DLLVERSTR