+dnl Copyright © 2021, 2023 Nick Bowler
+dnl
+dnl License WTFPL2: Do What The Fuck You Want To Public License, version 2.
+dnl This is free software: you are free to do what the fuck you want to.
+dnl There is NO WARRANTY, to the extent permitted by law.
+
+dnl DX_CHECK_SYSLOG
+dnl
+dnl Expands AC_CHECK_HEADERS([syslog.h])
+dnl
+dnl Then, if syslog.h is available, checks that a program can be linked
+dnl against the syslog family of functions.
+dnl
+dnl If successful, the cache variable dx_cv_have_syslog is set to "yes".
+dnl Otherwise, dx_cv_have_syslog is set to "no".
+AC_DEFUN([DX_CHECK_SYSLOG],
+[AC_CHECK_HEADERS([syslog.h], [], [], [@&t@])
+AS_IF([test x"$ac_cv_header_syslog_h" = x"yes"],
+ [AC_CACHE_CHECK([for syslog], [dx_cv_have_syslog],
+ [AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <syslog.h>],
+[openlog("conftest", LOG_PID, LOG_USER);
+syslog(LOG_ERR, "%s", "hello");
+closelog();])], [dx_cv_have_syslog=yes], [dx_cv_have_syslog=no])])])
+AS_IF([test x"$dx_cv_have_syslog" = x"yes"],
+ [AC_DEFINE([HAVE_SYSLOG], [1],
+ [Define to 1 if syslog et al. are available.])])])