[Cmake] -I/usr/include needed before -I/usr/X11R6/include

[Wheeler, Fred (Research)]

I need to have -I/usr/include before -I/usr/X11R6/include on the c++ compile command so I get GL/*.h
from /usr/include/GL, and not /usr/X11R6/include/GL.  Is there a way to specify this in cmake?  I
tried the following

  INCLUDE_DIRECTORIES( /usr/include ) # ignored

  ADD_DEFINITIONS( -I/usr/include )   # goes to end, after all of the other -I options

Thanks,
Fred Wheeler