Test/Validate OpenGL Vendor Neutral Dispatch Library (GLVND)

[gdevenyi]

cmake have been complaining for a while about:
https://cmake.org/cmake/help/latest/policy/CMP0072.html

https://cmake.org/cmake/help/latest/module/FindOpenGL.html#linux-specific

This is the "standard" way now, to have multiple OpenGL renderers available (like software intel + software + NVidida) on a single machine, even on a per-application basis. This is needed for doing things like x2go Display with software rendering and nvidia "optimus".

FreeGLUT will build against it, https://bugs.gentoo.org/721006

I suspect the rest will as well, we just need to not get in the way of the cmake FindOpenGL features providing the appropriate library choices if available (it falls back to LEGACY if GLVND isn't available).

[gdevenyi]

Display should probably drop its (old?) FindOpenGL.cmake
https://github.com/BIC-MNI/Display/blob/develop/cmake-modules/FindOpenGL.cmake
and FindGLUT.cmake
https://github.com/BIC-MNI/Display/blob/develop/cmake-modules/FindGLUT.cmake

[gdevenyi]

minimal modern 3.10.x example, https://stackoverflow.com/a/53378631/4130016