message: cmake: allow FFmpeg linking on Android
  details:
  In order to help CMake and PkgConfig find FFmpeg you need to:
  1) export `PKG_CONFIG_LIBDIR=${SYSROOT}`
  where `SYSROOT=${ANDROID_NDK}/sysroot`
  2) Add `-DCMAKE_PREFIX_PATH=${FFMPEG_INSTALL_PREFIX}`
  3) Append `-DCMAKE_FIND_ROOT_PATH=${FFMPEG_INSTALL_PREFIX}`
diff: @@ -255,8 +255,8 @@ OCV_OPTION(WITH_EIGEN "Include Eigen2/Eigen3 support" (NOT CV_DISABLE_OPTIMIZATI
  OCV_OPTION(WITH_VFW "Include Video for Windows support (deprecated, consider using MSMF)" OFF
  VISIBLE_IF WIN32
  VERIFY HAVE_VFW)
  -OCV_OPTION(WITH_FFMPEG "Include FFMPEG support" ON
  - VISIBLE_IF NOT ANDROID AND NOT IOS AND NOT WINRT
  +OCV_OPTION(WITH_FFMPEG "Include FFMPEG support" (NOT ANDROID)
  + VISIBLE_IF NOT IOS AND NOT WINRT
  VERIFY HAVE_FFMPEG)
  OCV_OPTION(WITH_GSTREAMER "Include Gstreamer support" ON
  VISIBLE_IF NOT ANDROID AND NOT IOS AND NOT WINRT
  