cmake: add WASAPI audio target to the build (thanks, Martin!).

Fixes Bugzilla #3588.

CMakeLists.txt

@@ -1075,6 +1075,7 @@ elseif(WINDOWS)
     check_include_file(dsound.h HAVE_DSOUND_H)
     check_include_file(dinput.h HAVE_DINPUT_H)
     check_include_file(xaudio2.h HAVE_XAUDIO2_H)
+    check_include_file(audioclient.h HAVE_AUDIOCLIENT_H)
     check_include_file(dxgi.h HAVE_DXGI_H)
     if(HAVE_D3D_H OR HAVE_D3D11_H OR HAVE_DDRAW_H OR HAVE_DSOUND_H OR HAVE_DINPUT_H OR HAVE_XAUDIO2_H)
       set(HAVE_DIRECTX TRUE)
@@ -1104,6 +1105,12 @@ elseif(WINDOWS)
       file(GLOB XAUDIO2_AUDIO_SOURCES ${SDL2_SOURCE_DIR}/src/audio/xaudio2/*.c)
       set(SOURCE_FILES ${SOURCE_FILES} ${XAUDIO2_AUDIO_SOURCES})
     endif()
+
+    if(HAVE_AUDIOCLIENT_H)
+      set(SDL_AUDIO_DRIVER_WASAPI 1)
+      file(GLOB WASAPI_AUDIO_SOURCES ${SDL2_SOURCE_DIR}/src/audio/wasapi/*.c)
+      set(SOURCE_FILES ${SOURCE_FILES} ${WASAPI_AUDIO_SOURCES})
+    endif()
   endif()
 
   if(SDL_VIDEO)

include/SDL_config.h.cmake

@@ -215,6 +215,7 @@
 #cmakedefine SDL_AUDIO_DRIVER_DISK @SDL_AUDIO_DRIVER_DISK@
 #cmakedefine SDL_AUDIO_DRIVER_DUMMY @SDL_AUDIO_DRIVER_DUMMY@
 #cmakedefine SDL_AUDIO_DRIVER_XAUDIO2 @SDL_AUDIO_DRIVER_XAUDIO2@
+#cmakedefine SDL_AUDIO_DRIVER_WASAPI @SDL_AUDIO_DRIVER_WASAPI@
 #cmakedefine SDL_AUDIO_DRIVER_DSOUND @SDL_AUDIO_DRIVER_DSOUND@
 #cmakedefine SDL_AUDIO_DRIVER_ESD @SDL_AUDIO_DRIVER_ESD@
 #cmakedefine SDL_AUDIO_DRIVER_ESD_DYNAMIC @SDL_AUDIO_DRIVER_ESD_DYNAMIC@