libclaw version 1.6.1-3 failed to build on amd64 with GCC-4.6/oneiric

libclaw version 1.6.1-3 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2456788

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/2456788/+files/buildlog_ubuntu-natty-amd64.libclaw_1.6.1-3_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 710 lines into the build log:

                 from /build/buildd/libclaw-1.6.1/./claw/ordered_set.hpp:33,
                 from /build/buildd/libclaw-1.6.1/./claw/arguments.hpp:35,
                 from /build/buildd/libclaw-1.6.1/./claw/arguments_table.hpp:34,
                 from /build/buildd/libclaw-1.6.1/./claw/application.hpp:33,
                 from /build/buildd/libclaw-1.6.1/claw/code/application.cpp:30:
/build/buildd/libclaw-1.6.1/./claw/avl_base.hpp:137:15: error: 'ptrdiff_t' does not name a type
/build/buildd/libclaw-1.6.1/./claw/avl_base.hpp:172:15: error: 'ptrdiff_t' does not name a type
make[3]: *** [CMakeFiles/claw_application.dir/claw/code/application.cpp.o] Error 1
make[3]: Leaving directory `/build/buildd/libclaw-1.6.1/build-tree'
make[2]: *** [CMakeFiles/claw_application.dir/all] Error 2
make[2]: Leaving directory `/build/buildd/libclaw-1.6.1/build-tree'
make[1]: *** [all] Error 2
make[1]: Leaving directory `/build/buildd/libclaw-1.6.1/build-tree'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110424-0146
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/libclaw-1.6.1