x11-links creates a shadow directory of symbolic links for X11 headers and
libraries to ${X11BASE} under ${PREFIX}/share/x11-links.

It is intended for use by buildlink code to cleanly separate out the true
X11 code files from any installed X11 package code files.  The X11
hierarchies supported are:

	XFree86-3.3.x
	XFree86-4.0.x
	XFree86-4.1.x
	XFree86-4.2.x
	XFree86-4.3.x