plasma-widget-message-indicator version 0.5.7-0ubuntu2 failed to build in oneiric

plasma-widget-message-indicator version 0.5.7-0ubuntu2 failed to build in oneiric
Link to failed build: https://launchpad.net/ubuntu/+archive/test-rebuild-20110816/+build/2708306

Details about the rebuild:
http://people.ubuntuwire.org/~wgrant/rebuild-ftbfs-test/test-rebuild-20110816-oneiric.html

Direct link to the build log: https://launchpad.net/ubuntu/+archive/test-rebuild-20110816/+build/2708306/+files/buildlog_ubuntu-oneiric-i386.plasma-widget-message-indicator_0.5.7-0ubuntu2_FAILEDTOBUILD.txt.gz

This log snippet might be of interest, since it triggered the matcher 'Purging chroot-autobuild'.
Excerpt 1386 lines into the build log:

Call Stack (most recent call first):
  /usr/share/kde4/apps/cmake/modules/FindPkgConfig.cmake:337 (_pkg_check_modules_internal)
  CMakeLists.txt:10 (pkg_check_modules)

CMake Error at /usr/share/kde4/apps/cmake/modules/FindPkgConfig.cmake:323 (message):
  pkg-config tool not found
Call Stack (most recent call first):
  /usr/share/kde4/apps/cmake/modules/FindPkgConfig.cmake:337 (_pkg_check_modules_internal)
  CMakeLists.txt:11 (pkg_check_modules)

-- Configuring incomplete, errors occurred!
make: *** [obj-i686-linux-gnu/CMakeCache.txt] Error 1
dpkg-buildpackage: error: debian/rules build gave error exit status 2
******************************************************************************
Build finished at 20110818-1225
FAILED [dpkg-buildpackage died]
Purging chroot-autobuild/build/buildd/plasma-widget-message-indicator-0.5.7