Update default audio device backends

[nanang]

Some platforms use PortAudio as their default audio device backend, while the PortAudio version we are using is quite old and the effort to update the version is not small. Meanwhile, we already have our own audio device implementations that are considerably lightweight and stable as they have been around and tested for quite long time. So yes, we are considering to update the default audio device backends to our own implementations.

• MacOSX
  Currently the default backend is PortAudio. since MacOSX 10.11, it produces warning message (thank you Martin Ohlsson for the report):

  WARNING:  140: This application, or a library it uses, is using the deprecated
  Carbon Component Manager for hosting Audio Units. Support for this will be
  removed in a future release. Also, this makes the host incompatible 
  with version 3 audio units. Please transition to the API's in AudioComponent.h
  

  So we'll update the default backend to our CoreAudio implementation.

• Linux/*nix
  The default is also PortAudio (ALSA or OSS), we'll use our ALSA implementation (if ALSA header is available).

• MinGW
  The default are both PortAudio and WMME, we'll just use WMME as default.

[nanang]

In 5197:

Close #1896: Update default audio device backend on MacOS to CoreAudio?.