title: How to Compile Opencv3.2.0 with opencv_contrib
body: <p>I use Centos7 and gcc is 4.8.5.I can not Comple extra modules from opencv_contrib like xfeatures2d for opencv3.2.0. I used<br>
  -D OPENCV_EXTRA_MODULES_PATH=../modules/opencv_contrib-3.x.x/modules Flag But I just get some errors like 
  opencv_contrib-3.0.0/modules/xfeatures2d/src/sift.cpp:340:5: error: ‘hal’  has not been declared
  Would you please help me how to install Opencv3.2 with xfeatures2d.</p>