tkgate version 1.8.7-2 failed to build on i386

tkgate version 1.8.7-2 failed to build on i386
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110329/+buildjob/2411940

Direct link to the build log: https://launchpad.net/ubuntu/+archive/test-rebuild-20110329/+buildjob/2411940/+files/buildlog_ubuntu-natty-i386.tkgate_1.8.7-2_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 1193 lines into the build log:

found X11/Xlib.h in: /usr/include

ERROR: Unable to find library X11

If you get this message, it may be because a required component
such as Tcl 8.0, Tk 8.0 or X11 was missing or could not be found.
See the section on 'NON STANDARD TCL/TK LOCATIONS' in the README
file for more information.
# Add here commands to compile the package.
/usr/bin/make
make[1]: Entering directory `/build/buildd/tkgate-1.8.7'
make[1]: *** No targets specified and no makefile found. Stop.
make[1]: Leaving directory `/build/buildd/tkgate-1.8.7'
make: *** [build-stamp] Error 2
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110408-1820
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/tkgate-1.8.7