clang16 throws an error because of the implicit function declaration of exit().
This leads to the wrong assumption that snprintf is not present on the system.

Bug: https://bugs.gentoo.org/906535
Upstream PR: https://sourceforge.net/p/log4cpp/codegit/merge-requests/10/

#  Pascal Jäger <pascal.jaeger@leimstift.de> (2023-09-22)

--- a/m4/AC_FUNC_SNPRINTF.m4
+++ b/m4/AC_FUNC_SNPRINTF.m4
@@ -12,7 +12,8 @@ dnl @author Caolan McNamara <caolan@skynet.ie>
 dnl
 AC_DEFUN([AC_FUNC_SNPRINTF],
 [AC_CACHE_CHECK(for working snprintf, ac_cv_func_snprintf,
-[AC_TRY_RUN([#include <stdio.h>
+[AC_TRY_RUN([#include <stdlib.h>
+#include <stdio.h>
 int main () { int l = snprintf(NULL,0,"%d",100); exit (!((3 <= l) || (-1 == l))); }
 ], ac_cv_func_snprintf=yes, ac_cv_func_snprintf=no,
 ac_cv_func_snprintf=no)])