fspanel version 0.7-9 failed to build on amd64 with GCC-4.6/oneiric

fspanel version 0.7-9 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2450377

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/2450377/+files/buildlog_ubuntu-natty-amd64.fspanel_0.7-9_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 996 lines into the build log:

/tmp/cc9rODxL.o: In function `move_taskbar':
/build/buildd/fspanel-0.7/fspanel.c:763: undefined reference to `XMoveWindow'
/tmp/cc9rODxL.o: In function `main':
/build/buildd/fspanel-0.7/fspanel.c:965: undefined reference to `XOpenDisplay'
/build/buildd/fspanel-0.7/fspanel.c:975: undefined reference to `XSelectInput'
/build/buildd/fspanel-0.7/fspanel.c:977: undefined reference to `XSetErrorHandler'
/build/buildd/fspanel-0.7/fspanel.c:979: undefined reference to `XInternAtoms'
/build/buildd/fspanel-0.7/fspanel.c:999: undefined reference to `XNextEvent'
/build/buildd/fspanel-0.7/fspanel.c:997: undefined reference to `XPending'
collect2: ld returned 1 exit status
make[1]: *** [fspanel] Error 1
make[1]: Leaving directory `/build/buildd/fspanel-0.7'
dh_auto_build: make -j1 returned exit code 2
make: *** [build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110422-1701
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/fspanel-0.7