openvpn-auth-ldap version 2.0.3-1 failed to build on amd64 with GCC-4.6/oneiric

openvpn-auth-ldap version 2.0.3-1 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2464151

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/2464151/+files/buildlog_ubuntu-natty-amd64.openvpn-auth-ldap_2.0.3-1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 506 lines into the build log:

gcc -o testplugin testplugin.o -export-dynamic -L. -lauth-ldap-testing -lldap -llber -lobjc
./libauth-ldap-testing.a(auth-ldap.o): In function `find_ldap_group':
/build/buildd/openvpn-auth-ldap-2.0.3/src/auth-ldap.m:418: undefined reference to `objc_msgSend'
/build/buildd/openvpn-auth-ldap-2.0.3/src/auth-ldap.m:418: undefined reference to `objc_msgSend'
/build/buildd/openvpn-auth-ldap-2.0.3/src/auth-ldap.m:419: undefined reference to `objc_msgSend'
/build/buildd/openvpn-auth-ldap-2.0.3/src/auth-ldap.m:424: undefined reference to `objc_msgSend'
/build/buildd/openvpn-auth-ldap-2.0.3/src/auth-ldap.m:424: undefined reference to `objc_msgSend'
./libauth-ldap-testing.a(auth-ldap.o):/build/buildd/openvpn-auth-ldap-2.0.3/src/auth-ldap.m:421: more undefined references to `objc_msgSend' follow
collect2: ld returned 1 exit status
make[2]: *** [testplugin] Error 1
make[2]: Leaving directory `/build/buildd/openvpn-auth-ldap-2.0.3/src'
make[1]: *** [all] Error 1
make[1]: Leaving directory `/build/buildd/openvpn-auth-ldap-2.0.3'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110425-0802
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/openvpn-auth-ldap-2.0.3