wmmixer version 1.6-1 failed to build in oneiric

wmmixer version 1.6-1 failed to build in oneiric
Link to failed build: https://launchpad.net/ubuntu/+source/wmmixer/1.6-1/+build/2648499

Details about the rebuild:
http://people.ubuntuwire.org/~wgrant/rebuild-ftbfs-test/test-rebuild-20110816-oneiric.html

Direct link to the build log: https://launchpad.net/ubuntu/+source/wmmixer/1.6-1/+build/2648499/+files/buildlog_ubuntu-oneiric-amd64.wmmixer_1.6-1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 1126 lines into the build log:

xhandler.o: In function `XHandler::init(int, char**, int)':
/build/buildd/wmmixer-1.6/xhandler.cc:60: undefined reference to `XOpenDisplay'
/build/buildd/wmmixer-1.6/xhandler.cc:62: undefined reference to `XDisplayName'
xhandler.o: In function `XHandler::initMask()':
/build/buildd/wmmixer-1.6/xhandler.cc:555: undefined reference to `XMapWindow'
wmmixer.o: In function `WMMixer::loop()':
/build/buildd/wmmixer-1.6/wmmixer.cc:52: undefined reference to `XPending'
/build/buildd/wmmixer-1.6/wmmixer.cc:54: undefined reference to `XNextEvent'
/build/buildd/wmmixer-1.6/wmmixer.cc:105: undefined reference to `XFlush'
collect2: ld returned 1 exit status
make[1]: *** [wmmixer] Error 1
make[1]: Leaving directory `/build/buildd/wmmixer-1.6'
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 20110727-1245
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/wmmixer-1.6