[Fontconfig] Upgrade strategy 2.1.0 -> 2.3.92

[Jim Osborn]

Many bits of my current environment (X-4.5.0, KDE-3.4.2, Qt-3.3.4)
were built against fontconfig 2.1.0. A typical ldd shows this:
  libfontconfig.so.1 => /usr/X11R6/lib/libfontconfig.so.1 (0x40850000)

The lib links are like this:
  libfontconfig.so.1 -> libfontconfig.so.1.0.

After building and installing fontconfig 2.3.92, I have a new lib:
  libfontconfig.so.1 -> libfontconfig.so.1.0.4

But I can't run my windowing system with the new lib; anything using
fontconfig crashes.  I can point libfontconfig.so.1 at the old lib and
run the old binaries.  (Ldconfig switches the link to point to the new
lib unless I give it the -X option, but I can live with ldconfig -X.)

I'm upgrading everything from sources and this is the first library
I've run into that uses the same version on its symlink (.so.1) to
point to an incompatible lib.  My question is: can I build Qt, KDE,
etc., to use the new fontconfig with that symlink pointing to the old
lib during the build process?  Will they run successfully when I get
everything built and point the link to the new lib?  All the various
pkg-config files are from the new versions of things, as are the
include files. 

If I need to have libfontconfig.so.1 -> libfontconfig.so.1.0.4
during the build process, can someone suggest a strategy to keep my
windowing system functional? 

Sorry to be asking such an elementary question, but since it takes a
few days to compile these things on this old machine, I'd rather do
as few false starts as possible.  

TIA,

Jim