xdriinfo doesn't build with nvidia-driver and WITH_NVIDIA_GL=yes

[John Nielsen]

Still following the upgrade procedure in the wiki, I set WITH_NVIDIA_GL=yes 
in /etc/make.conf and then did "make all install clean" from 
ports/x11/xorg. The xdriinfo build failed because of some missing GL header 
files. I un-set WITH_NVIDIA_GL and uninstalled nvidia-driver so I could 
install libGL and then it worked fine.

JN