morse-x version 20040713 failed to build on amd64 with GCC-4.6/oneiric

morse-x version 20040713 failed to build on amd64 with GCC-4.6/oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110413/+buildjob/2462434

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/2462434/+files/buildlog_ubuntu-natty-amd64.morse-x_20040713_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 430 lines into the build log:

main.c:(.text+0x280): undefined reference to `XFlush'
main.c:(.text+0x2a0): undefined reference to `XCreateGC'
main.c:(.text+0x2bd): undefined reference to `XGetKeyboardControl'
main.c:(.text+0x2d4): undefined reference to `XAutoRepeatOff'
main.c:(.text+0x2f2): undefined reference to `XSelectInput'
main.c:(.text+0x30e): undefined reference to `XAutoRepeatOn'
main.c:(.text+0x327): undefined reference to `XFreeGC'
main.c:(.text+0x340): undefined reference to `XUnmapWindow'
main.c:(.text+0x359): undefined reference to `XDestroyWindow'
main.c:(.text+0x36d): undefined reference to `XCloseDisplay'
collect2: ld returned 1 exit status
make[1]: *** [all] Error 1
make[1]: Leaving directory `/build/buildd/morse-x-20040713'
make: *** [build] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110424-1752
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/morse-x-20040713