Programs running with libc5 look for their timezone files in /usr/lib/zoneinfo, but the files are now in /usr/share/zoneinfo. So, a symlink is needed. Also when the TZ environment variable is not set the local timezone is expected in /usr/lib/zoneinfo/localtime rather than the current location of /etc/localtime. Again a symlink solves the problem. I think both symlinks should be part of the libc5 package since they are needed for the proper function of some libc5-using programs.
We cannot add a symlink to replace a directory in rpm because of the way in which rpm performs an upgrade: the new package (with the symlink) is installed before the old package (with the directory) is removed. That means that either the symlink can't be created because the directory exists during the install or the symlink is created in the directory that is then removed. The work around is to create the symlinks manually.