readline 6.3 fix from upstream

https://bugs.ruby-lang.org/issues/9578
--- ./ext/readline/readline.c	(revision 45224)
+++ ./ext/readline/readline.c	(revision 45225)
@@ -1974,7 +1974,7 @@
 
     rl_attempted_completion_function = readline_attempted_completion_function;
 #if defined(HAVE_RL_PRE_INPUT_HOOK)
-    rl_pre_input_hook = (Function *)readline_pre_input_hook;
+    rl_pre_input_hook = (rl_hook_func_t *)readline_pre_input_hook;
 #endif
 #ifdef HAVE_RL_CATCH_SIGNALS
     rl_catch_signals = 0;