cmake-mode.el: Replace use of obsolete function (since Emacs 24.3).

Auxiliary/cmake-mode.el

@@ -271,7 +271,7 @@ optional argument topic will be appended to the argument list."
     (save-selected-window
       (select-window (display-buffer buffer 'not-this-window))
       (cmake-mode)
-      (toggle-read-only t))
+      (read-only-mode 1))
     )
   )