Silence some compilation warnings

* lisp/emacs-lisp/check-declare.el (compilation-forget-errors):
* lisp/emulation/cua-base.el (delete-active-region):
* lisp/net/net-utils.el (w32-get-console-output-codepage):
* lisp/term/ns-win.el (ns-own-selection-internal)
(ns-disown-selection-internal, ns-selection-owner-p)
(ns-selection-exists-p, ns-get-selection):
Declare for compiler..

lisp/emacs-lisp/check-declare.el

@@ -284,6 +284,8 @@ TYPE is a string giving the nature of the error.  Warning is displayed in
                              type)
                      nil check-declare-warning-buffer)))
 
+(declare-function compilation-forget-errors "compile" ())
+
 (defun check-declare-files (&rest files)
   "Check veracity of all `declare-function' statements in FILES.
 Return a list of any errors found."