WaE: declared with greater visibility than the type of its field

To be specific, 'vcl::PageSyncData' declared with greater visibility
than the type of its field 'vcl::PageSyncData::mActions'

Adding a SAL_DLLPRIVATE to the PageSyncData struct, too, then.

Warning was emitted by g++ 4.2.1 against the MacOSX 10.6 SDK.

vcl/source/gdi/pdfextoutdevdata.cxx

@@ -298,7 +298,7 @@ void GlobalSyncData::PlayGlobalActions( PDFWriter& rWriter )
     }
 }
 
-struct PageSyncData
+struct SAL_DLLPRIVATE PageSyncData
 {
     std::deque< PDFExtOutDevDataSync >              mActions;
     std::deque< Rectangle >                         mParaRects;