title: OpenCV 3.0 videoio error
body: <p>I tried to compile OpenCV 3.0 alpha library for Qt Creator 5.4 with CMake 3.1.0, but I have error:</p>
  
  <pre><code>[ 44%] Building CXX object modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap
  _dshow.cpp.obj
  D:\opencv\sources\modules\videoio\src\cap_dshow.cpp:122:11: error: base class 's
  truct IUnknown' has accessible non-virtual destructor [-Werror=non-virtual-dtor]
  
   interface IEnumPIDMap : public IUnknown
             ^
  D:\opencv\sources\modules\videoio\src\cap_dshow.cpp:141:11: error: base class 's
  truct IUnknown' has accessible non-virtual destructor [-Werror=non-virtual-dtor]
  
   interface IMPEG2PIDMap : public IUnknown
             ^
  D:\opencv\sources\modules\videoio\src\cap_dshow.cpp:231:11: error: base class 's
  truct IUnknown' has accessible non-virtual destructor [-Werror=non-virtual-dtor]
  
   interface ISampleGrabberCB : public IUnknown
             ^
  D:\opencv\sources\modules\videoio\src\cap_dshow.cpp:245:11: error: base class 's
  truct IUnknown' has accessible non-virtual destructor [-Werror=non-virtual-dtor]
  
   interface ISampleGrabber : public IUnknown
             ^
  cc1plus.exe: some warnings being treated as errors
  modules\videoio\CMakeFiles\opencv_videoio.dir\build.make:150: recipe for target
  'modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_dshow.cpp.obj' failed
  mingw32-make[2]: *** [modules/videoio/CMakeFiles/opencv_videoio.dir/src/cap_dsho
  w.cpp.obj] Error 1
  CMakeFiles\Makefile2:2719: recipe for target 'modules/videoio/CMakeFiles/opencv_
  videoio.dir/all' failed
  mingw32-make[1]: *** [modules/videoio/CMakeFiles/opencv_videoio.dir/all] Error 2
  
  makefile:136: recipe for target 'all' failed
  mingw32-make: *** [all] Error 2
  </code></pre>
  
  <p>I selected:</p>
  
  <pre><code>CMAKE --&gt; CMAKE_BUILD_TYPE = Debug
  WITH --&gt; WITH_EIGEN = 0
  WITH --&gt; WITH_OPENGL = 0
  WITH --&gt; WITH_IPP = 0
  </code></pre>
  
  <p>The rest of settings is default. My OS is Windows 7 64 bit. OpenCV library source: <a href="http://sourceforge.net/projects/opencvlibrary/files/opencv-win/3.0.0-alpha/">http://sourceforge.net/projects/opencvlibrary/files/opencv-win/3.0.0-alpha/</a> </p>
  
  <p>What is wrong? Any ideas?</p>