https://github.com/tats/w3m/pull/248

From cecac3d8a177362fc27c8a109ac23a8760e74a10 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Mon, 12 Sep 2022 18:41:28 +0100
Subject: [PATCH] acinclude.m4: fix configure tests broken with Clang 15
 (implicit function declarations)

Clang 15 makes implicit function declarations fatal by default which
leads to some configure tests silently failing/returning
the wrong result.

Signed-off-by: Sam James <sam@gentoo.org>
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -904,7 +904,8 @@ AC_DEFUN([AC_W3M_SIGSETJMP],
 [AC_SUBST(HAVE_SIGSETJMP)
 AC_MSG_CHECKING(for sigsetjmp)
 AC_TRY_COMPILE(
-[#include <setjmp.h>],
+[#include <setjmp.h>
+ #include <stdlib.h>],
 [ jmp_buf env;
    if (sigsetjmp(env, 1) != 0) { exit(0); } siglongjmp(env, 1);],
 [have_sigsetjmp="yes"; AC_DEFINE(HAVE_SIGSETJMP)],