xorg-libraries question/problem

[walt]

I'm getting compile errors from the kdebase3 port due to missing symbol 
errors from libXdmcp.so (part of the xorg-libraries).

Two of the missing symbols are XdmcpWrap and XdmcpUnwrap which are defined
(or not) depending on whether HASXDMAUTH is defined.  Take a look at
/usr/X11R6/include/X11/Xdmcp.h for details.
The libraries libXdmcp.so and libXdmcp.a do NOT define those two
symbols, so I assume that HASXDMAUTH was undefined during the
compilation of the xorg-libraries.
I don't understand the point of exluding those symbols from the
libraries and including the symbols in the header file since
it provides an opportunity for errors just like the one I'm
seeing with kdebase3.
Now part B of the puzzle:  I have a FreeBSD-4 machine with XFree86
which has only a libXdmcp.a (no .so on the machine) and another
 FreeBSD-CURRENT machine (with xorg) which has both the .a and
. so libraries and all three of those libraries define those two
missing symbols.
Can anyone give me the big picture here?  What determines
whether a .so library is built in addition to the .a lib.
Why, in general, would I NOT want to build the .so also?
And, in particular, anyone know why those two symbols
were not compiled into libXdmcp (i.e. why HASXDMAUTH
was defined for FreeBSD but not DFly)?  Why would anyone
*want* to exclude those symbols in the first place.
Long question, sorry.