Clang16 will not allow implicit function declaration, implicit int etc. by default.
This patch overhauls the source code to build with clan16 defaults.

Bug: https://bugs.gentoo.org/874960

Original patch by Pascal Jäger <pascal.jaeger@leimstift.de>,
minor adjustments by Hanno Böck.

diff -Naurp a/inews/clientlib.c b/inews/clientlib.c
--- a/inews/clientlib.c	1996-06-06 21:41:07.000000000 +0200
+++ b/inews/clientlib.c	2022-11-26 18:32:09.383423565 +0100
@@ -14,6 +14,7 @@ static char	*sccsid = "@(#)clientlib.c	1
 #include "../config.h"
 #endif
 
+#include <arpa/inet.h>
 #include <stdio.h>
 #ifndef FOR_NN
 #include <sys/types.h>
@@ -52,6 +53,7 @@ static char	*sccsid = "@(#)clientlib.c	1
 #endif
 
 #include "nntp.h"
+#include "clientlib.h"
 
 FILE	*ser_rd_fp = NULL;
 FILE	*ser_wr_fp = NULL;
@@ -133,7 +135,7 @@ char	*file;
  *			for reading and writing to server.
  */
 
-server_init(machine)
+int server_init(machine)
 char	*machine;
 {
 	int	sockt_rd, sockt_wr;
@@ -194,7 +196,7 @@ char	*machine;
  *	Errors:		Printed via perror.
  */
 
-get_tcp_socket(machine)
+int get_tcp_socket(machine)
 char	*machine;
 {
 	int	s;
@@ -218,7 +220,6 @@ char	*machine;
         * fails.
         */
        if( (hp = gethostbyname( machine ) ) == NULL ) {
-               unsigned long inet_addr();
                static struct hostent def;
                static struct in_addr defaddr;
                static char *alist[1];
@@ -344,7 +345,7 @@ char	*machine;
  *	Errors:		Printed via nerror.
  */
 
-get_dnet_socket(machine)
+int get_dnet_socket(machine)
 char	*machine;
 {
 	int	s, area, node;
@@ -427,7 +428,7 @@ char	*machine;
  *	Side effects:	None.
  */
 
-handle_server_response(response, server)
+int handle_server_response(response, server)
 int	response;
 char	*server;
 {
@@ -502,7 +503,7 @@ char *string;
  *	Side effects:	Talks to server, changes contents of "string".
  */
 
-get_server(string, size)
+int get_server(string, size)
 char	*string;
 int	size;
 {
diff -Naurp a/inews/clientlib.h b/inews/clientlib.h
--- a/inews/clientlib.h	1996-06-06 21:41:07.000000000 +0200
+++ b/inews/clientlib.h	2022-11-26 18:27:59.711248861 +0100
@@ -9,3 +9,7 @@ extern	int	server_init();
 extern	void	put_server();
 extern	int	get_server();
 extern	void	close_server();
+
+extern	int	get_tcp_socket(char *machine);
+extern	int	get_server(char *string, int size);
+extern	int	handle_server_response(int response, char *server);
diff -Naurp a/inews/inews.c b/inews/inews.c
--- a/inews/inews.c	2004-01-29 03:14:19.000000000 +0100
+++ b/inews/inews.c	2022-11-26 18:32:26.200435328 +0100
@@ -39,15 +39,20 @@ static char *sccsid = "@(#)inews.c	1.16
 
 #include "conf.h"
 #include "nntp.h"
+#include "clientlib.h"
 
 
 #define	MAX_SIGNATURE	6
 
+int strneql(char *a, char *b, int n);
+void gen_frompath(void);
+int valid_header(register char *h);
+
 extern	FILE	*ser_wr_fp;
 
 char	host_name[256];
 
-main(argc, argv)
+int main(argc, argv)
 int	argc;
 char	*argv[];
 {
@@ -254,7 +259,7 @@ append_signature()
  * a From: line in it.
  */
 
-gen_frompath()
+void gen_frompath()
 {
 	char	*full_name;
 	char	*cp;
@@ -330,7 +335,7 @@ gen_frompath()
  *	Side effects:	None.
  */
 
-strneql(a, b, n)
+int strneql(a, b, n)
 register char *a, *b;
 int	n;
 {