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.