mdadm version 3.1.4-1+8efb9d1ubuntu5 failed to build in oneiric

mdadm version 3.1.4-1+8efb9d1ubuntu5 failed to build in oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110816/+build/2704931

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/+archive/test-rebuild-20110816/+build/2704931/+files/buildlog_ubuntu-oneiric-i386.mdadm_3.1.4-1%2B8efb9d1ubuntu5_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 513 lines into the build log:

make[1]: Entering directory `/build/buildd/mdadm-3.1.4'
dh_testdir
/usr/bin/make CXFLAGS="-ggdb -Wno-strict-aliasing -fomit-frame-pointer -Os" CONFFILE=/tmp/mdadm.conf all
make[2]: Entering directory `/build/buildd/mdadm-3.1.4'
gcc -Wall -Werror -Wstrict-prototypes -Wextra -Wno-unused-parameter -ggdb -Wno-strict-aliasing -fomit-frame-pointer -Os -DSendmail=\""/usr/sbin/sendmail -t"\" -DCONFFILE=\"/tmp/mdadm.conf\" -DCONFFILE2=\"/etc/mdadm.conf\" -DMAP_DIR=\"/dev/.mdadm\" -DMAP_FILE=\"map\" -DMDMON_DIR=\"/dev/.mdadm\" -DUSE_PTHREADS -DDEBIAN -c -o mdadm.o mdadm.c
mdadm.c: In function 'main':
mdadm.c:105:6: error: variable 'auto_update_home' set but not used [-Werror=unused-but-set-variable]
cc1: all warnings being treated as errors

make[2]: *** [mdadm.o] Error 1
make[2]: Leaving directory `/build/buildd/mdadm-3.1.4'
make[1]: *** [mdadm.udeb] Error 2
make[1]: Leaving directory `/build/buildd/mdadm-3.1.4'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110818-0223
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/mdadm-3.1.4