cmb.bundle.unix: skip libcrypt again
This library is used by glibc plugins (namely Kerberos authentication)
and, as such, must be provided by the system. Newer distros may have
issues with the code built against our CI platform's older libcrypt
and may need to install compatibility packages.
@john.tourtellott We may need to just up the build platform for your projects; the skew between the security libraries and our old base isn't going to get any smaller over time.