extcalc version 0.9.2-1 failed to build on amd64 with GCC-4.6/oneiric

extcalc version 0.9.2-1 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2449620

Details about the rebuild:
https://lists.ubuntu.com/archives/ubuntu-devel/2011-April/033042.html

Direct link to the build log: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2449620/+files/buildlog_ubuntu-natty-amd64.extcalc_0.9.2-1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 24245 lines into the build log:

graphsetdialog.o: In function `QString':
/usr/share/qt3/include/qstring.h:842: undefined reference to `QString::shared_null'
graphsetdialog.o: In function `QValueListNode':
/usr/share/qt3/include/qvaluelist.h:66: undefined reference to `QString::QString(QString const&)'
graphsetdialog.o: In function `QValueListNode':
/usr/share/qt3/include/qstring.h:842: undefined reference to `QString::makeSharedNull()'
collect2: ld returned 1 exit status
make[3]: *** [extcalc] Error 1
make[3]: Leaving directory `/build/buildd/extcalc-0.9.2/src'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/build/buildd/extcalc-0.9.2'
make[1]: *** [all] Error 2
make[1]: Leaving directory `/build/buildd/extcalc-0.9.2'
make: *** [debian/stamp-makefile-build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110422-1208
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/extcalc-0.9.2