Made samples build independent from nonfree module.

(cherry picked from commit bba8c0beac)

samples/cpp/freak_demo.cpp

@@ -34,15 +34,27 @@
 //  or tort (including negligence or otherwise) arising in any way out of
 //  the use of this software, even if advised of the possibility of such damage.
 
+#include "opencv2/opencv_modules.hpp"
 #include <iostream>
-#include <string>
-#include <vector>
 
-#include <opencv2/core/core.hpp>
-#include <opencv2/highgui/highgui.hpp>
-#include <opencv2/features2d/features2d.hpp>
-#include <opencv2/nonfree/features2d.hpp>
-#include <opencv2/legacy/legacy.hpp>
+#ifndef HAVE_OPENCV_NONFREE
+
+int main(int, char**)
+{
+    std::cout << "The sample requires nonfree module that is not available in your OpenCV distribution." << std::endl;
+    return -1;
+}
+
+#else
+
+# include <string>
+# include <vector>
+
+# include <opencv2/core/core.hpp>
+# include <opencv2/highgui/highgui.hpp>
+# include <opencv2/features2d/features2d.hpp>
+# include <opencv2/nonfree/features2d.hpp>
+# include <opencv2/legacy/legacy.hpp>
 
 using namespace cv;
 
@@ -126,3 +138,5 @@ int main( int argc, char** argv ) {
     imshow("matches", imgMatch);
     waitKey(0);
 }
+
+#endif