https://github.com/zmanda/amanda/pull/220

From 74610ac5522caa779b30323f1c731775083c5bbc Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Fri, 14 Apr 2023 15:45:16 +0200
Subject: [PATCH] configure: Avoid an implicit int in the IPv6 test

Otherwise, the test fails unconditionally with compilers that
do not support implicit ints (a language feature that was removed with
the C99 language revision).
--- a/config/amanda/ipv6.m4
+++ b/config/amanda/ipv6.m4
@@ -85,7 +85,7 @@ AC_DEFUN([AMANDA_CHECK_IPV6],
 #include <sys/socket.h>
 #include <errno.h>
 
-main()
+int main(void)
 {
    int aa;
    aa = socket(AF_INET6, SOCK_STREAM, 0);