Before this change, the build would duplicate the prefix in the
installation location for cgi-bin stuff:
-- Installing: /nix/store/skg6b81hikd3fvvdf62xbkm6gsbid41a-zoneminder-1.32.3/nix/store/skg6b81hikd3fvvdf62xbkm6gsbid41a-zoneminder-1.32.3/libexec/zoneminder/cgi-bin/zms