x86 support

[hatharry]

fix for issue #83

[soredake]

[387/388] Linking _build-x86/mpv
/mpv-android/buildscripts/prefix/x86/usr/local/lib/libavformat.so: error: undefined reference to 'ff_aptx_demuxer'
collect2: error: ld returned 1 exit status

[jeeb]

@soredake thanks for spotting this breakage in FFmpeg :) (learned through @sfan5 ) . Recently added demuxer had a bug where its definition depended on the muxer, which is why linking failed when muxers were intentionally disabled. It's now fixed in FFmpeg upstream.

[sfan5]

merged 983ceaf