Silence some vc compilation warnings

Silence some vc compilation warnings

* lisp/vc/vc-arch.el (vc-exec-after): Declare.
(vc-switches): Autoload.

* lisp/vc/vc-bzr.el: No need to require vc when compiling.
(vc-exec-after, vc-set-async-update, vc-default-dir-printer)
(vc-resynch-buffer, vc-dir-refresh): Declare.
(vc-setup-buffer, vc-switches): Autoload.

* lisp/vc/vc-dir.el (desktop-missing-file-warning): Declare.

* lisp/vc/vc-mtn.el (vc-exec-after): Declare.
(vc-switches): Autoload.

* lisp/vc/vc-rcs.el (vc-expand-dirs, vc-switches)
(vc-tag-precondition, vc-buffer-sync, vc-rename-master): Autoload.
(vc-file-tree-walk): Declare.

* lisp/vc/vc-svn.el (vc-exec-after): Declare.
(vc-switches, vc-setup-buffer): Autoload.

* lisp/obsolete/vc-mcvs.el (vc-checkout, vc-switches, vc-default-revert):
Autoload.
(vc-resynch-buffer): Declare.