Fix function prototype warnings for C23 compatibility

- Add proper function prototypes: fatal(), my_exit(), set_order()
- Fix function pointer types to match call sites: void (*func)(int)
- Remove conflicting localtime() declaration in rip.c
- Fix incorrect new_item() call in state.c (remove unused argument)

Result: Zero compilation warnings, C23 compatible.

See MODERNIZATION_LOG.md for detailed analysis.

potions.c

@@ -17,7 +17,7 @@
 typedef struct
 {
     int pa_flags;
-    void (*pa_daemon)();
+    void (*pa_daemon)(int);
     int pa_time;
     char *pa_high, *pa_straight;
 } PACT;