Port to C23. Correct error handler type, use system bool
https://bugs.gentoo.org/944095
https://bugs.gentoo.org/944399
--- a/bdfgrab.c
+++ b/bdfgrab.c
@@ -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;
--- a/hbf.c
+++ b/hbf.c
@@ -62,6 +62,7 @@
 #include <stdio.h>
 #include <ctype.h>
 #include <string.h>
+#include <stdbool.h>
 #include "hbf.h"
 
 #ifdef __MSDOS__
@@ -82,9 +83,8 @@
 
 #define	reg	register
 
-typedef	int	bool;
-#define	TRUE	1
-#define	FALSE	0
+#define	TRUE	true
+#define	FALSE	false
 
 #define	Bit(n)	(1<<(7 - (n)))