DKMS systemd startup service has been removed, modules building is now handled by alpm hooks at install time. Startup modules loading must be done via modules-load.d.

su

mcedit /usr/share/libalpm/hooks/rebuild.hook

Paste this in using [shift] + [insert] keys:

[Trigger]
Operation = Upgrade
Type = Package
Target = *

[Action]
Description = Upgrade trigger
When = PostTransaction
Depends = coreutils
Exec = /bin/echo ‘Checking if any package needs rebuilding.’

Save using [F2] key and close using [F10].

For more info run man libalpm or visit here.

Cheers.

Andrzej