rename: modernize replacement

rename: modernize replacement

* modules/rename (Depends-on): Add stdio.
(configure.ac): Declare witness.
* m4/rename.m4 (gl_FUNC_RENAME): Ensure dependency order, and let
stdio take care of replacement.
* m4/stdio_h.m4 (gl_STDIO_H_DEFAULTS): Add new defaults.
* modules/stdio (Makefile.am): Substitute them.
* lib/stdio.in.h (rename): Declare replacement.
* lib/rename.c (includes): Allow cross-compilation to non-windows
machines.
* doc/posix-functions/rename.texi (rename): Improve
documentation.

Signed-off-by: Eric Blake <ebb9@byu.net>