Enable core dumps in Apache

Enable core dumps in Apache

I would like to enable core dumps in my Apache web server.
Since I have PHP 5.5 and OPcache my Mediawiki site crashes with the
following error:
child pid ... exit signal Segmentation fault (11)
So I would like to get more information through the core dump.
I created a directory: /tmp/apache-coredump owned by http:http (my apache
user and group) and with the 777 rights.
I added to the httpd.conf file:
CoreDumpDirectory "/tmp/apache-coredump"
But, now (with the CoreDumpDirectory instruction) my Apache server crashes
on start-up:
sudo systemctl restart httpd
Job for httpd.service failed.
See 'systemctl status httpd.service' and 'journalctl -xn' for details.
The journal give me the following info
apachectl[4149]: CoreDumpDirectory /tmp/apache-coredump does not exist
I checked, the directory exist 0_°
Without the CoreDumpDirectory instruction, there is no core dump generated
in the ServerRoot (/etc/httpd) directory.
I'm on Archlinux 3.10.6-2 64-bits with Apache/2.2.25 Prefork