* configure.in: Simplify/fix systemd detection: move later to fix
  autoconf warnings; define HAVE_SYSTEMD rather than using CPPFLAGS.

* server/listen.c: Use HAVE_SYSTEMD for systemd #define.

* modules/arch/unix/config5.m4: Update systemd headers check.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1528032 13f79535-47bb-0310-9956-ffa450edef68