Specific Options
The following directories, or symbolic links to directories, must be in /usr/include, if the corresponding subsystem is installed:
The symbolic link /usr/include/X11 must link to /usr/X11R6/include/X11 if the latter exists.
The following directories, or symbolic links to directories, must be in /usr/include, if the corresponding subsystem is installed:
The symbolic link /usr/include/X11 must link to /usr/X11R6/include/X11 if the latter exists.