Cleaning up for -Wredundant-decls

[Dmitry Antipov]

Since it's quite typical for a mature project to have global namespace polluted
with old unused and duplicated declarations, I would like to enable 
-Wredundant-decls
when --enable-gcc-warnings is turned on. This task may be accomplished in three 
steps:

00) Tweak make-docfile to avoid EXFUN anywhere except generated globals.h,
    and change DEFUN to avoid conflict with EXFUN;
01) Fix components comes from gnulib;
02) Fix the rest, offloading lisp.h where possible.

If there is a chance that 01) will be incorporated into gnulib and there are no
objections for the rest, I'll do 00) and 02) as proposed in the patches below.

Dmitry

00_base_Wredundant_decls.patch
Description: Text Data

01_lib_Wredundant_decls.patch
Description: Text Data

02_common_Wredundant_decls.patch
Description: Text Data