Remove libsystemd dependency from main httpd binary

Remove libsystemd dependency from main httpd binary

Until this change httpd was linking libsystemd to the main httpd binary. If you want to run lightweight version of httpd in container, sometimes you just want to install
httpd binary with as little dependencies as possible to make container small in size and do not pull uncencessary dependencies and libraries.

This change will move all systemd library calls from listen.c to mod_systemd module and remove systemd linking from the main httpd bin.
Fixed mixed declaration and wrongly declared variable.

Submitted by: Luboš Uhliarik <luhliari redhat.com>

Github: closes #312

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1899784 13f79535-47bb-0310-9956-ffa450edef68