To clarify this for people – this isn’t a CMAKE flag, it’s an environment variable (the picture above looks like a cmake-gui window to me? But maybe it’s a gui environment variable editor).
So for example, on my Ubuntu machine, I can set the variable with:
CYCLES_OPTIX_TEST="all" and then, when I run Blender from this console, it will have access to this environment variable, and I’ll be able to attempt to use Optix with my GTX card (works beautifully on GTX1080). Now, if I want to make this persistent so that I don’t have to set the variable everytime, I can
export CYCLES_OPTIX_TEST and it will be saved as an environmental variable.
This works on the build-bot builds, ever since the commit was added.
I hope this helps people who were confused, like me. Thanks @LazyDodo for helping me over at Blender.chat, and for making the commit.
edit: am a idiot.
./blender runs blender