rbldnsd version 0.996b failed to build on amd64 with GCC-4.6/oneiric

rbldnsd version 0.996b failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2467165

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/2467165/+files/buildlog_ubuntu-natty-amd64.rbldnsd_0.996b_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 320 lines into the build log:

checking for ranlib... ranlib
checking for stdint.h... yes
checking for inline... yes
checking for socklen_t... yes
checking for libraries needed for connect()... ok (none needed)
checking for IPv6... yes
checking for mallinfo()... yes
checking for poll()... yes
checking for vsnprintf()... yes
checking for writev()/readv()... yes
checking for setitimer()... yes
checking for zlib support... no
configure: fatal: zlib support is requested but not found/available
make: *** [config.h] Error 1
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110426-0633
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/rbldnsd-0.996b