From http://kojipkgs.fedoraproject.org/packages/sed/4.2.1/1.fc11/data/logs/i586/build.log checking for library containing setfilecon... no configure: WARNING: This system supports SELinux but libselinux is missing. configure: WARNING: sed will be compiled without SELinux support. Indeed, libselinux-devel does not show up in http://kojipkgs.fedoraproject.org/packages/sed/4.2.1/1.fc11/data/logs/i586/root.log
Still present in rawhide: http://kojipkgs.fedoraproject.org/packages/sed/4.2.1/2.fc12/data/logs/i686/build.log
This bug appears to have been reported against 'rawhide' during the Fedora 12 development cycle. Changing version to '12'. More information and reason for this action is here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
Fixed in sed 4.2.1-4.