Building ffmpeg executable on Android

Current versions of build scripts do not create ffmpeg and ffprobe binaries but it is possible to generate them by applying the following changes.

In build/android-ffmpeg.sh

1. Delete --disable-programs line

2. Change --disable-static line to --enable-static

3. Change --enable-shared line to --disable-shared

After applying these changes, android.sh will create ffmpeg and ffprobe binaries under the prebuilt/android-<arch>/ffmpeg/bin path.

Please note that snappy, tesseract and x265 libraries need to be linked with a c++ library and scripts are configured to use libc++_shared.so. So if you enable them, you need to copy libc++_shared.so as well.