fix(audio): unbreak bluetooth audio - no sound, and freeze on disconnect

[dalexanco]

Two bugs, one cause. Over a bluetooth headset games had no sound at all, and disconnecting the headset mid-game froze the emulator for good.

alsa-lib guards every PCM with a recursive lock, and on the bluealsa sink that lock is never released once the PCM is open. SDL's audio thread blocks inside libasound and never runs our callback - that is the silence. The freeze follows from it: on disconnect minarch resets the audio device from the game loop, and SDL_CloseAudioDevice() waits forever for that stuck thread to exit.

LIBASOUND_THREAD_SAFE=0 fixes both. SDL already serialises opening and closing a device against its own audio thread, so alsa's internal locking buys us nothing.

The same lock is why SND_quit() was commented out, with a note blaming SDL stream reconnection: closing the device on exit hit the same deadlock. It works now, so the call comes back at the end of main(). It stays out of Core_unload(), which runs while the core is still loaded and can still emit audio into the buffer SND_quit() frees.

Tested on a Brick (tg5040): sound in the headset, no freeze on disconnect, clean exit back to the launcher, and audio still fine on the next launch.

#810

[frysee]

I'm not ready yet to touch BT again, it has only been three months or so. Its an absolute clusterfuck to get right. 💀

[frysee]

We will revisit this after h700 lands, maybe together with !736.