Android cpp dependency

As explained in official Android c++ support guide, libc++ is not a system library and it must be included in your apk if you use it.

MobileFFmpeg includes five external libraries which depend on libc++. These libraries are openh264, rubberband, snappy, tesseract and x265. When either of these five libraries is enabled during compilation, libc++_shared.so library is added into mobile-ffmpeg.aar archive created.

Additionally, MobileFFmpeg release packages that include these libraries (video, full and all gpl licensed packages) contain libc++_shared.so library as well.