WaE: 'updateChecksum' overrides a member function but is not marked 'override'

Change-Id: Ic2230e1d1f54e27d4189fc56b525a7e76ddab649
(cherry picked from commit a5493ee2)

vcl/inc/opengl/salbmp.hxx

@@ -53,7 +53,7 @@ private:
     std::deque< OpenGLSalBitmapOp* >    maPendingOps;
 
     void makeCurrent();
-    virtual void updateChecksum() const;
+    virtual void updateChecksum() const SAL_OVERRIDE;
 
     bool calcChecksumGL(OpenGLTexture& rInputTexture, ChecksumType& rChecksum) const;