Earlier quoted context omitted.
That makes no sense. Which Common Lisp implementations contain a compiler written in C or Fortran?
I should have been clearer: written partially in C or Fortran. SBCL, for example, has C bindings in the /runtime subdirectory.
So nothing to do with SBCL's compiler (which is somewhat confusingly named 'Python' and written entirely in Lisp), then.