Repository: opencv
Issue: Failed to build iOS framework with --dynamic --legacy_build arguments.
Labels: bug,category: build/install,platform: ios/osx

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##### System information (version)
<!-- Example
- OpenCV => 4.2
- Operating System / Platform => Windows 64 Bit
- Compiler => Visual Studio 2017
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- OpenCV => 4.5.2
- Operating System / Platform => macOS Catalina 10.15.7
- Xcode => 12.2
- cmake => 3.20.0
- platform => iOS

##### Detailed description

<!-- your description -->
Failed to build iOS framework with --dynamic --legacy_build arguments.

##### Steps to reproduce

<!-- to add code example fence it with triple backticks and optional file extension
    ```.cpp
    // C++ code example
    ```
 or attach as .txt or .zip file
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`python opencv/platforms/ios/build_framework.py --contrib opencv_contrib --dynamic --legacy_build ios`

```
Undefined symbols for architecture armv7:
  "_kCVPixelBufferCGImageCompatibilityKey", referenced from:
      -[CvVideoCamera pixelBufferFromCGImage:] in libopencv_world.a(cap_ios_video_camera.o)
  "_OBJC_CLASS_$_CALayer", referenced from:
      objc-class-ref in libopencv_world.a(cap_ios_video_camera.o)
  "_CGAffineTransformMakeRotation", referenced from:
      -[CvVideoCamera adjustLayoutToInterfaceOrientation:] in libopencv_world.a(cap_ios_video_camera.o)
      -[CvVideoCamera layoutPreviewLayer] in libopencv_world.a(cap_ios_video_camera.o)
  "_OBJC_CLASS_$_AVCaptureStillImageOutput", referenced from:
      objc-class-ref in libopencv_world.a(cap_ios_photo_camera.o)

```

All results are here.
[log.txt](https://github.com/opencv/opencv/files/6288418/log.txt)


However, when the --legacy_build argument was excluded, the iOS framework was successfully built.
`python opencv/platforms/ios/build_framework.py --contrib opencv_contrib --dynamic ios`

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