Without those data files HRTF will silently fail to initialize.
It searches /usr and /usr/local by default but we don't have those paths.
It also searches XDG_DATA_DIRS but using that requires configuration by the
user. This patch makes makes it just work.
How to play with it:
- Build `mpv` with `openalSoft` support.
- cat << EOF > ~/.alsoftrc
[general]
hrtf = true
EOF
- Wear stereo headphones.
- Play a file with 6 or more channels with `mpv -ao openal $file`, e.g.
https://archive.org/download/5.1SurroundSoundTestFilesVariousFormatsAACAC3MP4DTSWAV/5.1%20Surround%20Sound%20AAC%20Test.mp4
- Try `hrtf = false` to hear the difference.
