redefines about which buildlink.mk files would care is BUILDLINK_X11_DIR,
which points to the location of the X11R6 hierarchy used during building.
If x11.buildlink.mk isn't included, then BUILDLINK_X11_DIR defaults to
${X11BASE} (set in bsd.pkg.mk), so its value is always safe to use. Remove
the ifdefs surrounding the use of BUILDLINK_X11_DIR in tk/buildlink.mk and
revert changes to move x11.buildlink.mk before the other buildlink.mk files.
use X11_BUILDLINK_MK as a test value. Generally just reordering the
inclusions so that x11.buildlink.mk comes before the other buildlink.mk
files will make everthing work.
