mooproxy version 0.1.3-1 failed to build on amd64 with GCC-4.6/oneiric

mooproxy version 0.1.3-1 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2462415

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/2462415/+files/buildlog_ubuntu-natty-amd64.mooproxy_0.1.3-1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 337 lines into the build log:

panic.c:98:8: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
panic.c:106:7: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
panic.c:107:7: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
panic.c:112:8: warning: ignoring return value of 'write', declared with attribute warn_unused_result [-Wunused-result]
cc -Wall -g -O2 -c -o recall.o recall.c
cc -Wall -lcrypt mooproxy.o misc.o config.o daemon.o world.o network.o command.o mcp.o log.o accessor.o timer.o resolve.o crypt.o line.o panic.o recall.o -o mooproxy
crypt.o: In function `prompt_to_md5hash':
/build/buildd/mooproxy-0.1.3/crypt.c:85: undefined reference to `crypt'
crypt.o: In function `match_string_md5hash':
/build/buildd/mooproxy-0.1.3/crypt.c:216: undefined reference to `crypt'
collect2: ld returned 1 exit status
make[1]: *** [mooproxy] Error 1
make[1]: Leaving directory `/build/buildd/mooproxy-0.1.3'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110424-1749
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/mooproxy-0.1.3