Patched to compile on Windows.

src/audio/SDL_sysaudio.h

@@ -191,6 +191,7 @@ extern AudioBootStrap ARTS_bootstrap;
 extern AudioBootStrap ESD_bootstrap;
 extern AudioBootStrap NACLAUDIO_bootstrap;
 extern AudioBootStrap NAS_bootstrap;
+extern AudioBootStrap WASAPI_bootstrap;
 extern AudioBootStrap XAUDIO2_bootstrap;
 extern AudioBootStrap DSOUND_bootstrap;
 extern AudioBootStrap WINMM_bootstrap;