[tlbuild] linking against expat ... why

[Karl Berry]

Regarding the xetex .so problems.  If anyone can develop an
understandable recipe for eliminating the unwanted secondary .so
dependencies, then by all means let us do so.

But flailing around compiling on a myriad of systems and hoping for a
good result seems pointless to me.  I'd rather stick with the binaries
we have, despite the .so problems -- which are nothing new, anyway.

karl