After further investigation, I noticed that the package libnvidia-nvvm4
was not installed on my system.
Installing It creates the libnvidia-nvvm files as described by Ole, and
creating a symlink allows Darktable to use OpenCL.
Thank you Ole !
I am not sure why this package was not installed, since I used OpenCL
under Darktable with nvidia-driver version 510. Maybe I uninstalled it
when tried to resolve the original issue.
I will have to make some image processing test to be sure that the
original reported problem is solved.
