mod_systemd is available since Apache 2.5.
The first thing you can do is to check the version of Apache you use apachectl -V
The second thing is to search a linux distribution, that distributes Apache 2.5
https://httpd.apache.org/docs/trunk/mod/mod_systemd.html
##Download and compile Apache
I recommend to do this in a testing environment. I've tested it on a debian minbase wheezy system. For arch linux the package names should be almost the same and instead of apt-get, pacman should be used.
#install build dependencies
> apt-get install subversion
> apt-get install autoconf
> apt-get install libtool
> apt-get install python
> apt-get install libexpat1-dev
> apt-get install libpcre3-dev
> apt-get install libsystemd-daemon-dev
> apt-get install g++
> apt-get install make
#download apache development source code
> mkdir trunk
> cd trunk
> svn co http://svn.apache.org/repos/asf/httpd/httpd/trunk ./
> svn co http://svn.apache.org/repos/asf/apr/apr/trunk srclib/apr
#configure apache
> ./buildconf
> ./configure
#build and install
> make install
#enable mod_systemd
> echo "LoadModule systemd_module modules/mod_systemd.so" >> /usr/local/apache2/conf/httpd.conf
#check enabled modules
> /usr/local/apache2/bin/apachectl -M