cmake: Resolve OpenGL policy warning.
cmake: Resolve OpenGL policy warning.

CMake now requires to set a GL library preference.
This patch sets the prefered library to `GLVND`, which is the modern
default behaviour.

See: `cmake --help-policy CMP0072`

GPUOpen-Tools/Compressonator,GPUOpen-Tools/Compressonator,GPUOpen-Tools/Compressonator,GPUOpen-Tools/Compressonator