fixed DLL linking of wxMessageOutput class

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@45526 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msgout.h

@@ -40,7 +40,11 @@ public:
     WX_DEFINE_VARARG_FUNC_VOID(Printf, DoPrintf)
 
 protected:
-    void DoPrintf(const wxChar* format, ...) ATTRIBUTE_PRINTF_2;
+    // NB: this is pure virtual so that it can be implemented in dllexported
+    //     wxMessagOutput class
+    virtual void DoPrintf(const wxChar* format, ...) ATTRIBUTE_PRINTF_2 = 0;
+
+    // called by DoPrintf() to output formatted string
     virtual void Output(const wxString& str) = 0;
 };
 
@@ -62,6 +66,10 @@ public:
     // sets the global wxMessageOutput instance; returns the previous one
     static wxMessageOutput* Set(wxMessageOutput* msgout);
 
+protected:
+    virtual void DoPrintf(const wxChar* format, ...) ATTRIBUTE_PRINTF_2;
+    virtual void Output(const wxString& str) = 0;
+
 private:
     static wxMessageOutput* ms_msgOut;
 };

src/common/msgout.cpp

@@ -76,7 +76,7 @@ wxMessageOutput* wxMessageOutput::Set(wxMessageOutput* msgout)
     return old;
 }
 
-void wxMessageOutputBase::DoPrintf(const wxChar* format, ...)
+void wxMessageOutput::DoPrintf(const wxChar* format, ...)
 {
     va_list args;
     va_start(args, format);