>: extern rtx gen_save_stack_function           PROTO((void));
>: extern rtx gen_restore_stack_function        PROTO((void));
>: 
>: in {insn-flags.h, insn-emit.c}.
>
>insn-flags.h is generated in your usr.bin/egcs/common/ directory, and NOT
>in src/gnu/dist/gcc, right?

Yes.

I guess the reason is:

rs6000.md has 

(define_expand "save_stack_function"
  [(use (const_int 0))]
  ""
  "")

(define_expand "restore_stack_function"
  [(use (const_int 0))]
  ""
  "")

and they don't have operands defined, so genemit makes them PROTO((void)).