hpanel version 0.3.2-1 failed to build on amd64 with GCC-4.6/oneiric

hpanel version 0.3.2-1 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2453142

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/2453142/+files/buildlog_ubuntu-natty-amd64.hpanel_0.3.2-1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 1137 lines into the build log:

/build/buildd/hpanel-0.3.2/hpanel.c:1214: undefined reference to `XSelectInput'
/build/buildd/hpanel-0.3.2/hpanel.c:1216: undefined reference to `XSetErrorHandler'
/build/buildd/hpanel-0.3.2/hpanel.c:1218: undefined reference to `XInternAtoms'
/build/buildd/hpanel-0.3.2/hpanel.c:1224: undefined reference to `XSync'
/build/buildd/hpanel-0.3.2/hpanel.c:1242: undefined reference to `XMoveWindow'
/build/buildd/hpanel-0.3.2/hpanel.c:1261: undefined reference to `XPending'
/build/buildd/hpanel-0.3.2/hpanel.c:1261: undefined reference to `XPending'
/build/buildd/hpanel-0.3.2/hpanel.c:1263: undefined reference to `XNextEvent'
collect2: ld returned 1 exit status
make[2]: *** [hpanel] Error 1
make[2]: Leaving directory `/build/buildd/hpanel-0.3.2'
make[1]: *** [override_dh_auto_build] Error 2
make[1]: Leaving directory `/build/buildd/hpanel-0.3.2'
make: *** [build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110423-1438
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/hpanel-0.3.2