GLVND appears to break the entire UI on ATI video cards.
It was set to GLVND due to an understanding that this was a no-op setting, but it turns
out the documentation in OpenGL_GL_PREFERENCE is confusing, and it looks like LEGACY
is the setting that was being used after all.
An additional point of interest is that debian/rules contained OpenGL_GL_PREFERENCE=GLVND,
and this was done back in the High Fidelity days. It's uncertain whether this was correct
or not, though.
This should be a no-op, besides generating less build warnings,
since:
"CMake 3.11 and above prefer to choose GLVND libraries."
And 3.11 is a few years old at this point
