use new readline function types (closes #20374)

Misc/NEWS

@@ -38,6 +38,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #20374: Fix build with GNU readline >= 6.3.
+
 - Issue #14548: Make multiprocessing finalizers check pid before
   running to cope with possibility of gc running just after fork.
   (Backport from 3.x.)

Modules/readline.c

@@ -911,12 +911,12 @@ setup_readline(void)
     rl_bind_key_in_map ('\t', rl_complete, emacs_meta_keymap);
     rl_bind_key_in_map ('\033', rl_complete, emacs_meta_keymap);
     /* Set our hook functions */
-    rl_startup_hook = (Function *)on_startup_hook;
+    rl_startup_hook = (rl_hook_func_t *)on_startup_hook;
 #ifdef HAVE_RL_PRE_INPUT_HOOK
-    rl_pre_input_hook = (Function *)on_pre_input_hook;
+    rl_pre_input_hook = (rl_hook_func_t *)on_pre_input_hook;
 #endif
     /* Set our completion function */
-    rl_attempted_completion_function = (CPPFunction *)flex_complete;
+    rl_attempted_completion_function = (rl_completion_func_t *)flex_complete;
     /* Set Python word break characters */
     completer_word_break_characters =
         rl_completer_word_break_characters =