emerging xfree doesn't create the symbolic link /usr/include/X11 -> /usr/X11R6/include/X11 this way lots of programs fail to emerge (the forum is full of "I'm missing Xlib.h - where is it?" messages). adding a line like "dosym /usr/X11R6/include/X11 /usr/include/X11" should fix this.
It is actually created in baselayout, but I added it to Xfree a few hours back.
this was fixed by azarah and is included in xfree-4.2.0-r12.ebuild,v 1.9 2002/07/17 19:04:21