Fix C23 problems.

--- gbdfed-1.6/bdfgrab.c	2010-04-16 15:39:01.000000000 +0100
+++ gbdfed-1.6/bdfgrab.c	2025-07-04 15:47:37.464636582 +0100
@@ -244,7 +244,7 @@
     XCharStruct *cp;
     bdf_property_t *pp, prop;
     bdf_callback_struct_t cb;
-    int (*old_error_handler)();
+    XErrorHandler old_error_handler;
 
     if (f == 0)
       return 0;
--- gbdfed-1.6/hbf.c	2010-04-16 15:39:07.000000000 +0100
+++ gbdfed-1.6/hbf.c	2025-07-04 15:48:07.180194181 +0100
@@ -82,9 +82,8 @@
 
 #define	reg	register
 
-typedef	int	bool;
-#define	TRUE	1
-#define	FALSE	0
+#define	TRUE	true
+#define	FALSE	false
 
 #define	Bit(n)	(1<<(7 - (n)))