Merge pull request opencv#14292 from alalek:issue_14291

* macosx: fix C++11 build

backporting commit c3cf35a

* macosx: eliminate build warning

Author: alalek

modules/highgui/src/window_cocoa.mm

@@ -266,7 +266,7 @@ CV_IMPL void cvResizeWindow( const char* name, int width, int height)
     CVWindow *window = cvGetWindow(name);
     if(window && ![window autosize]) {
         height += [window contentView].sliderHeight;
-        NSSize size = { width, height };
+        NSSize size = { (CGFloat)width, (CGFloat)height };
         [window setContentSize:size];
     }
     [localpool drain];

modules/videoio/src/cap_avfoundation_mac.mm

@@ -181,7 +181,7 @@ - (IplImage*)getOutput;
                 double fps, CvSize frame_size,
                 int is_color=1);
         ~CvVideoWriter_AVFoundation();
-        bool writeFrame(const IplImage* image);
+        bool writeFrame(const IplImage* image) CV_OVERRIDE;
         int getCaptureDomain() const CV_OVERRIDE { return cv::CAP_AVFOUNDATION; }
     private:
         IplImage* argbimage;