echo-area-clear-hook definition?

[Pavel Janík]

Hi,

the variable echo-area-clear-hook is not defined as other Lisp variables in
keyboard.c (DEFVAR_LISP is #if 0'ed to provide doc-string, but the symbol
itself is not defined by DEFVAR_LISP):

#if 0
  DEFVAR_LISP ("echo-area-clear-hook", ...,
               doc: /* Normal hook run when clearing the echo area.  */);
#endif
  Qecho_area_clear_hook = intern ("echo-area-clear-hook");
  SET_SYMBOL_VALUE (Qecho_area_clear_hook, Qnil);

Can you please tell me what is the reason?
-- 
Pavel Janík

panic("Tell me what a watchpoint trap is, and I'll then
deal with such a beast...");
                  -- 2.2.16 arch/arch/sparc/kernel/traps.c