Tcllibc is a helper package a user normally will not have to deal with. It is especially not necessary to load it explicitly, to the contrary, this is not recommended.
Instead, a number of packages in Tcllib are automatically checking for its presence and will load it if available, to accelerate their operation.
As such the commands it provides may implement public and/or internal interfaces of the package in question. Whichever, they are commands which do not need documentation here.
The packages using Tcllibc are:
As a last note: While the Tcllibc binary has been built using Critcl, it is not Critcl itself. Critcl is not distributed with ActiveTcl.