Maybe cl-runtime, or cl-rt?

We need a (require 'cl-<something>) which brings up CL but only within
the "cl-" namespace.  I don't have a good idea for naming.  `cl-defs'
might be OK, but I'm open to other suggestions.  Maybe `cl-layer', or
`cl-emu', or `cl-compat'?
`cl-funs' is another option, indeed.