[MIDIPlay] Add option to switch different audio backends

[WUGqnwvMQPzl]

Since commit acd361e, the midi play utility adds audio backend for ALSA, though it also disables SDL audio backend for unix systems.

In typical Linux desktop setup, most users don't use bare ALSA for audio, but paired with PulseAudio or Pipewire, which blocks lower level PCM devices, results adlmidiplay couldn't play the midi and exits:

%  adlmidiplay CANYON.MID 
==========================================
         libADLMIDI demo utility
==========================================

 - Library version 1.6.2
 - Nuked OPL3 (v 1.8) Emulator in use
 - Number of chips 4
 - Number of four-ops 0
 - Track count: 1
 - Volume model: Audio Interface Library (AIL)
 - Channel allocation mode: <auto>
 - Gain level: 2
 - Automatic arpeggio is turned OFF
 - File [CANYON.MID] opened!
 - Loop is turned ON

==========================================
Playing... Hit Ctrl+C to quit!

ERROR: Couldn't open audio: ALSA ERROR: Can't open "default" PCM device. Device or resource busy

currently a workaround is install ALSA configuration package for PulseAudio or Pipewire, and pass ALSAPCM=pulse or ALSAPCM=pipewire environment variable to adlmidiplay.

But the SDL audio backend, to me, it just works, and I like to have an option to switch different audio backends, and have ability to fallback to other working audio backend, if possible.

[Wohlstand]

Hello! Ye, I thinking about making something like. Primarily I added bare ALSA use to build the player for single-board PC with Buildroot environment that offers only ALSA. But to have the thing work better I need to handle more different backends too like PulseAudio and libsndio. Or for now I can set the ALSA backend as a build fallback when no SDL2 or 3 is installed.

[Wohlstand]

As a quick solution I added an option to prefer SDL Audio in any way. And I think, I'll better try to make a primitive audio playback library so it's will be easy to share it between libADLMIDI and libOPNMIDI, and with an ability to use multiple backends. I want to have such primitive audio library to make library less depend on large libraries, but SDL2/SDL3 will still be supported as a fallback API on new platforms.