all KDE app builds fail

[Andrew Schulman <andrex@alumni.utexas.net>]

I upgraded to KDE 3.1.3, in Debian unstable.  This includes libqt3c102-mt
and all the related build packages: libqt3-mt-dev, kdelibs4-dev, and
libqt3-compat-headers.  I also upgraded my gcc to version 3.2.2.

Now whenever I try to build a KDE app from source (e.g. kgpg, kopete,
knowit), I get the infamous error message

# ./configure --with-qt-dir=/usr/share/qt3
<snip>
checking for Qt... configure: error: Qt (>= Qt 3.0.3) (library qt-mt) not
found. Please check your installation!
For more details about this problem, look at the end of config.log.
Make sure that you have compiled Qt with thread support!

But libqt-mt.so is present:

# ls -l /usr/share/qt3/lib/libqt-mt.so*
lrwxr-xr-x    1 root     root           30 Sep 13 00:14 /usr/share/qt3/lib/
libqt-mt.so -> ../../../lib/libqt-mt.so.3.2.1
lrwxr-xr-x    1 root     root           30 Sep  5 18:18 /usr/share/qt3/lib/
libqt-mt.so.3 -> ../../../lib/libqt-mt.so.3.2.1
lrwxr-xr-x    1 root     root           30 Sep  5 18:18 /usr/share/qt3/lib/
libqt-mt.so.3.2 -> ../../../lib/libqt-mt.so.3.2.1
# ls -l /usr/lib/libqt-mt.so.3.2.1
-rw-r--r--    1 root     root      6571312 Sep  3 13:18 /usr/lib/
libqt-mt.so.3.2.1

Here's the source of the failure from config.log:

configure:21754: rm -rf SunWS_cache; g++ -o conftest -Wnon-virtual-dtor
-Wno-long-long -Wundef -Wall -pedantic -W -Wpointer-arith
-Wmissing-prototypes -Wwrite-strings -ansi -D_XOPEN_SOURCE=500
-D_BSD_SOURCE -Wcast-align -Wconversion -O2 -fno-exceptions -fno-check-new
-I/usr/share/qt3/include -I/usr/X11R6/include  -DQT_THREAD_SUPPORT 
-D_REENTRANT  -L/usr/share/qt3/lib -L/usr/X11R6/lib
  conftest.cc  -lqt-mt -lpng -lz -lm -ljpeg -ldl  -lXext -lX11 -lSM -lICE 
-lpthread 1>&5
/tmp/ccYZnuRb.o(.text+0xb): In function `main':
: undefined reference to `QString::null'
/tmp/ccYZnuRb.o(.text+0x10): In function `main':
: undefined reference to `QStyleFactory::create(QString const &)'

and so on.  There's a whole string of undefined references.  Since I
upgraded, all of my builds fail in exactly this way.

I've seen many people asking about this same problem in the newsgroups. 
Almost all of the responders advise adding some combination of

export QTDIR=/usr/share/qt3
--with-qt-includes=/usr/include/qt3
--with-qt-dir=/usr/share/qt3
--with-qt-libs=/usr/lib/qt3

to the configure command.  Some of these have worked for me in the past, but
none of them do now.  Also note that -L/usr/share/qt3/lib and -I/usr/share
qt3/include are on the gcc command line, and the error messages complain
about missing references, not missing files.  So gcc is finding the files,
but they're not providing the right definitions.

Another common piece of advice is that the app source must be broken.  That
may be so for some apps, but can it be true for every KDE app that I build? 
They all fail, in exactly the same way.  And Google tells me that a lot of
other people are suffering from the same problem right now.

I'd be grateful to anyone who can help me solve this problem!
Andrew.