Move wxBell() from base to core library.

This allows to get rid of ugly preprocessor checks due to the fact that this
function could be defined in one or the other library depending on the port
used and also fix a problem with it being defined differently in the base
library depending on which GUI port (Carbon or Cocoa) was used under OS X.
It also fixes the problem with wxBell() in wxGTK under Windows.

Closes #14406.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71797 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/utils.h

@@ -192,6 +192,8 @@ bool wxIsBusy();
     @note This function is categorized as a GUI one and so is not thread-safe.
 
     @header{wx/utils.h}
+
+    @library{wxcore}
 */
 void wxBell();