crossroads version 2.65-1 failed to build on i386

crossroads version 2.65-1 failed to build on i386
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110329/+buildjob/2390476

Direct link to the build log: https://launchpad.net/ubuntu/+archive/test-rebuild-20110329/+buildjob/2390476/+files/buildlog_ubuntu-natty-i386.crossroads_2.65-1_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 2976 lines into the build log:

Making: ./build
make[4]: Entering directory `/build/buildd/crossroads-2.65/xr/build'
make[4]: Nothing to be done for `class-compile'.
make[4]: Leaving directory `/build/buildd/crossroads-2.65/xr/build'
ar rs build/libxr.a */*.o
ar: creating build/libxr.a
ranlib build/libxr.a
make[3]: Leaving directory `/build/buildd/crossroads-2.65/xr'
/usr/bin/make build/xr
make[3]: Entering directory `/build/buildd/crossroads-2.65/xr'
/usr/bin/g++-4.5 -O3 -g -o build/xr \
   -Lbuild -lxr
build/libxr.a(thread_start.o): In function `Thread::start()':
/build/buildd/crossroads-2.65/xr/ThreadsAndMutexes/thread/start.cc:22: undefined reference to `pthread_create'
/build/buildd/crossroads-2.65/xr/ThreadsAndMutexes/thread/start.cc:22: undefined reference to `pthread_create'
/build/buildd/crossroads-2.65/xr/ThreadsAndMutexes/thread/start.cc:22: undefined reference to `pthread_create'
collect2: ld returned 1 exit status
make[3]: *** [build/xr] Error 1
make[3]: Leaving directory `/build/buildd/crossroads-2.65/xr'
make[2]: *** [foo] Error 2
make[2]: Leaving directory `/build/buildd/crossroads-2.65/xr'
make[1]: *** [local] Error 2
make[1]: Leaving directory `/build/buildd/crossroads-2.65'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110403-1108
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/crossroads-2.65