The descriptions of the dev-cpp/commoncpp2, dev-libs/commonc++, and dev-libs/commonc++2 packages contain "forthreading" instead of "for threading".
Created attachment 37388 [details, diff] commoncpp2 ebuild patch
Created attachment 37389 [details, diff] commonc++ ebuild patch
Created attachment 37390 [details, diff] commonc++2 ebuild patch
The above patches to the respective ebuilds should do the trick. (They did for me.)
Fixed in CVS. Thanks for the bug report.