[mpv] please use x86-v3 build.

[enihcam]

nearly all Windows systems running MPV have x86-v3 instructions that accelerate video processing.

e.g.:
https://sourceforge.net/projects/mpv-player-windows/files/release/mpv-0.37.0-x86_64-v3.7z/download

[AeliusSaionji]

I'm adhering to the provided release builds, which are not offered with v3 :/