portlint -C ok,
poudriere bulk with OPTIONS_SET=NVIDIA_GL ok
poudriere bulk with OPTIONS_UNSET=NVIDIA_GL ok
Caveats:
* Building emulators/linux-c6 with NVIDIA_GL enabled needs OVERRIDE_LINUX stuff,
otherwise it will conflict due to nvidia-driver pulling in linux_base-f10.
* Likewise, building emulators/linux-f10 with OVERRIDE_LINUX stuff set to c6 AND
NVIDIA_GL enabled won't be possible.