Toggle Compilation Shell minor mode.
With a prefix argument ARG, enable Compilation Shell minor mode
if ARG is positive, and disable it otherwise. If called from
Lisp, enable the mode if ARG is omitted or nil.
When Compilation Shell minor mode is enabled, all the
error-parsing commands of the Compilation major mode are
available but bound to keys that don't collide with Shell mode.
See `compilation-mode'.
(fn &optional ARG)