Another attempt to return ao_sndio to mpv

https://github.com/mpv-player/mpv/pull/9298

Index: audio/out/ao.c
--- audio/out/ao.c.orig
+++ audio/out/ao.c
@@ -41,6 +41,7 @@ extern const struct ao_driver audio_out_audiounit;
 extern const struct ao_driver audio_out_coreaudio;
 extern const struct ao_driver audio_out_coreaudio_exclusive;
 extern const struct ao_driver audio_out_rsound;
+extern const struct ao_driver audio_out_sndio;
 extern const struct ao_driver audio_out_pulse;
 extern const struct ao_driver audio_out_jack;
 extern const struct ao_driver audio_out_openal;
@@ -87,6 +88,9 @@ static const struct ao_driver * const audio_out_driver
 #endif
 #if HAVE_SDL2_AUDIO
     &audio_out_sdl,
+#endif
+#if HAVE_SNDIO
+    &audio_out_sndio,
 #endif
     &audio_out_null,
 #if HAVE_COREAUDIO
