https://github.com/radvd-project/radvd/commit/f4baa88bfd77710a6034e3c23b95ef5efb80f83b
https://bugs.gentoo.org/880823

From ff7ab0cf445236f30e58531175ba912614fed952 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Thu, 17 Nov 2022 22:03:25 +0000
Subject: [PATCH 1/2] Makefile.am: drop -Wno-implicit-function-declaration

1. Clang 16 makes -Wimplicit-function-declaration error by default
   (and it's planned that GCC 14 will do the same) so we need to fix
   the real problem. This is papering over it.

2. It's not true that there's nothing we can do about it. Fix in a follow-up
   commit.

Bug: https://bugs.gentoo.org/880823
Fixes: b5e6b09cf914a960ac3b1676b77d3ea9f91821c7
Signed-off-by: Sam James <sam@gentoo.org>
--- a/Makefile.am
+++ b/Makefile.am
@@ -66,9 +66,6 @@ radvd_LDADD = \
 scanner.c: gram.h
 gram.h: gram.c
 
-libradvd_parser_a_CFLAGS = \
-	-Wno-implicit-function-declaration
-
 libradvd_parser_a_SOURCES = \
 	gram.h \
 	gram.y \

From e0f5bcd9091a5f7abd423fce9f372c8079849a64 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Thu, 17 Nov 2022 22:03:25 +0000
Subject: [PATCH 2/2] gram.y: Fix -Wimplicit-function-declaration

Clang 16 makes -Wimplicit-function-declaration an error by default.

For more information, see LWN.net [0] or LLVM's Discourse [1], the Gentoo wiki [2],
or the (new) c-std-porting mailing list [3].

[0] https://lwn.net/Articles/913505/
[1] https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213
[2] https://wiki.gentoo.org/wiki/Modern_C_porting
[3] hosted at lists.linux.dev.

Bug: https://bugs.gentoo.org/880823
Signed-off-by: Sam James <sam@gentoo.org>
--- a/gram.y
+++ b/gram.y
@@ -20,6 +20,10 @@
 
 #define YYERROR_VERBOSE 1
 
+int yylex (void);
+void yyset_in (FILE * _in_str);
+int yylex_destroy (void);
+
 #if 0 /* no longer necessary? */
 #ifndef HAVE_IN6_ADDR_S6_ADDR
 # ifdef __FreeBSD__