All the files under /usr/lib/sendmail-cf are architecture-independ macro-files and should go to %{_datadir}/sendmail-cf. Because the sendmail-cf package contains these files only, it's buildarch should be changed to `noarch' also.
noarch can only be done in subpackages. But /usr/share will be done for the next bigger update of sendmail, as this is not too imortant.
guess that it should be "doable" so far that RPM can set subpackages to a different architecture than the main package. if it is not currently possible on rpm (guess it is not but who knows without taking a look) it would be closed as deferred at least. if rpm is not allowed to do such a packages this would be a nice reason for a patch ;)
cf files are now in /usr/share Florian La Roche