Steel Bank Common Lisp

The following error shows up during (asdf:oos 'asdf:compile-op :mcclim
 :force T):

 ; /usr/lib/sbcl/sb-bsd-sockets/split.fasl written
 ; compilation finished in 0:00:00
 (/usr/lib/sbcl/sb-bsd-sockets/constants.lisp
  /usr/lib/sbcl/sb-bsd-sockets/constants.fasl
  /usr/lib/sbcl/sb-bsd-sockets/constants.fasl
  /usr/lib/sbcl/sb-bsd-sockets/foo.c
  /usr/lib/sbcl/sb-bsd-sockets/a.out
  /usr/lib/sbcl/sb-bsd-sockets/constants.lisp-temp)

 debugger invoked on a SIMPLE-ERROR in thread #<THREAD "initial thread"
 {A8EC631}>:
   The CC environment variable has not been set in SB-GROVEL. Since this
   variable should always be set during the SBCL build process, this might
   indicate an SBCL with a broken contrib installation.


Exporting CC before starting sbcl fixed the problem.
What _is_ the official way to force recompilation of just one system?


 TIA Ralf Mattes