resolve the DLL linking problems with MSVC due to use of static variables of template types by replacing them by a non-template unique untypedNullDataPtr

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@56638 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/string.cpp

@@ -50,6 +50,18 @@
     #define wxStringStrlen   wxStrlen
 #endif
 
+// ----------------------------------------------------------------------------
+// global variables
+// ----------------------------------------------------------------------------
+
+namespace wxPrivate
+{
+
+static UntypedBufferData s_untypedNullData(NULL);
+
+UntypedBufferData * const untypedNullDataPtr = &s_untypedNullData;
+
+} // namespace wxPrivate
 
 // ---------------------------------------------------------------------------
 // static class variables definition
@@ -2096,3 +2108,4 @@ int wxString::Freq(wxUniChar ch) const
     }
     return count;
 }
+