No changes, just extract wxCreateHiddenWindow() declaration in a header.

Add wx/msw/private/hiddenwin.h with wxCreateHiddenWindow() declaration instead
of declaring it manually in all the files using it.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69170 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/dialup.cpp

@@ -40,6 +40,7 @@
 #include "wx/generic/choicdgg.h"
 
 #include "wx/msw/private.h"
+#include "wx/msw/private/hiddenwin.h"
 #include "wx/dynlib.h"
 
 wxDEFINE_EVENT( wxEVT_DIALUP_CONNECTED, wxDialUpEvent );
@@ -66,10 +67,6 @@ wxDEFINE_EVENT( wxEVT_DIALUP_DISCONNECTED, wxDialUpEvent );
 #define INTERNET_CONNECTION_PROXY 4
 #endif
 
-// implemented in utils.cpp
-extern "C" WXDLLIMPEXP_BASE HWND
-wxCreateHiddenWindow(LPCTSTR *pclassname, LPCTSTR classname, WNDPROC wndproc);
-
 static const wxChar *
     wxMSWDIALUP_WNDCLASSNAME = wxT("_wxDialUpManager_Internal_Class");
 static const wxChar *gs_classForDialUpWindow = NULL;