https://gitlab.freedesktop.org/dbus/dbus/-/merge_requests/339

From 88c96ff6a351758cb7c69a25e3a8464b5164a19c Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Mon, 12 Sep 2022 18:37:35 +0100
Subject: [PATCH] configure.ac: 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/configure.ac
+++ b/configure.ac
@@ -613,7 +613,8 @@ AS_IF([test -n "$dbus_va_copy_func"],
 AC_CACHE_CHECK([whether $CC knows __sync_sub_and_fetch()],
   dbus_cv_sync_sub_and_fetch,
   [AC_LINK_IFELSE([
-     AC_LANG_PROGRAM([[]], [[int a = 4; int b = __sync_sub_and_fetch(&a, 4); exit(b); ]])],
+     AC_LANG_PROGRAM([[]], [[#include <stdlib.h>
+     int a = 4; int b = __sync_sub_and_fetch(&a, 4); exit(b); ]])],
      [dbus_cv_sync_sub_and_fetch=yes],
      [dbus_cv_sync_sub_and_fetch=no])
   ])
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