Created attachment 171642 [details]
It seems I overlooked this port when creating a patch for 6.8 :)
The attached patch fixes the build.
The patch was incomplete, as it did not add the files for CentOS 6.8, nor the src rpms.
The bigger question however is if we still need this port, since it was based on CentOS 6.4
A commit references this bug:
Date: Wed Jun 22 09:22:16 UTC 2016
New revision: 417295
Remove old Linux DRI port. The newer version in graphics/linux-c6-dri
should just work nowadays.