Fix Unix build with libSDL 2 in debug mode.

SDL_AudioDriverName() was replaced with SDL_GetCurrentAudioDriver() in SDL v2.

Closes #15271.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74271 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775