Add compatibility code when GLVND is not available
CMake's FindOpenGL internally handles EGL only correctly when GLVND is available. This might not the case on embedded systems and actually it is not necessary when EGL::EGL is found.
CMake's FindOpenGL internally handles EGL only correctly when GLVND is available. This might not the case on embedded systems and actually it is not necessary when EGL::EGL is found.