backport the WXDLLIMPEXP_FWD_XXX macros to 2.8 (patches 1822143 and 1822146)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@49563 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/utils.h

@@ -23,8 +23,8 @@
     #include "wx/gdicmn.h"
 #endif
 
-class WXDLLIMPEXP_BASE wxArrayString;
-class WXDLLIMPEXP_BASE wxArrayInt;
+class WXDLLIMPEXP_FWD_BASE wxArrayString;
+class WXDLLIMPEXP_FWD_BASE wxArrayInt;
 
 // need this for wxGetDiskSpace() as we can't, unfortunately, forward declare
 // wxLongLong