Thanks for mentioning me!
Genefer does not run for me under opencl-mesa either.
Under opecl-mesa, from primegrid only pps_sieve of would run.
Milkyway worked only under opencl-amd (which is userspace part of closed amdgpupro, with radeon opensource kernel module).
I have not tested Primegrid on opencl-mesa-git nor on opencl-amd.
I never succeeded in installing fglrx nor full amdgpupro drivers.