audio: add build options for audio backend support

The added build options USE_ALSA, USE_LIBAO, USE_OSS and USE_PULSEAUDIO allow to
enable/disable specific audio backends in the build. This provides more control
over the used dependencies.

The OSS backend wasn't enabled in the previous build configuration, consequently
the build option USE_OSS is set to OFF by default.

CMakeLists.txt

@@ -65,6 +65,10 @@ option(USE_DX11 "Build with Direct3D 11 support" ON)
 option(LIBRETRO "Build libretro core" OFF)
 option(USE_OPENGL "Use OpenGL API" ON)
 option(USE_VIDEOCORE "RPI: use the legacy Broadcom GLES libraries" OFF)
+option(USE_ALSA "Build with ALSA support" ON)
+option(USE_LIBAO "Build with AO support" ON)
+option(USE_OSS "Build with OSS support" OFF)
+option(USE_PULSEAUDIO "Build with PulseAudio support" ON)
 option(USE_BREAKPAD "Build and link with breakpad library" ON)
 option(ENABLE_GDB_SERVER "Build with GDB debugging support" OFF)
 option(ENABLE_DC_PROFILER "Build with support for target machine (SH4) profiler" OFF)
@@ -411,11 +415,17 @@ if(USE_VULKAN)
 endif()
 
 if(NOT LIBRETRO)
-	find_package(ALSA)
-	if(ALSA_FOUND AND NOT ANDROID)
-		target_compile_definitions(${PROJECT_NAME} PRIVATE USE_ALSA)
-		target_include_directories(${PROJECT_NAME} PRIVATE ${ALSA_INCLUDE_DIRS})
-		target_link_libraries(${PROJECT_NAME} PRIVATE ${ALSA_LIBRARIES})
+	if(USE_OSS)
+		target_compile_definitions(${PROJECT_NAME} PRIVATE USE_OSS)
+	endif()
+
+	if(USE_ALSA)
+		find_package(ALSA)
+		if(ALSA_FOUND AND NOT ANDROID)
+			target_compile_definitions(${PROJECT_NAME} PRIVATE USE_ALSA)
+			target_include_directories(${PROJECT_NAME} PRIVATE ${ALSA_INCLUDE_DIRS})
+			target_link_libraries(${PROJECT_NAME} PRIVATE ${ALSA_LIBRARIES})
+		endif()
 	endif()
 
 	if(MINGW)
@@ -489,10 +499,12 @@ endif()
 
 find_package(PkgConfig)
 if(PKG_CONFIG_FOUND AND NOT ANDROID AND NOT APPLE AND NOT LIBRETRO)
-	pkg_check_modules(AO IMPORTED_TARGET ao)
-	if(AO_FOUND)
-		target_compile_definitions(${PROJECT_NAME} PRIVATE USE_LIBAO)
-		target_link_libraries(${PROJECT_NAME} PRIVATE PkgConfig::AO)
+	if(USE_LIBAO)
+		pkg_check_modules(AO IMPORTED_TARGET ao)
+		if(AO_FOUND)
+			target_compile_definitions(${PROJECT_NAME} PRIVATE USE_LIBAO)
+			target_link_libraries(${PROJECT_NAME} PRIVATE PkgConfig::AO)
+		endif()
 	endif()
 
 	if(NOT SDL2_FOUND)
@@ -509,10 +521,12 @@ if(PKG_CONFIG_FOUND AND NOT ANDROID AND NOT APPLE AND NOT LIBRETRO)
 		endif()
 	endif()
 
-	pkg_check_modules(LIBPULSE IMPORTED_TARGET libpulse)
-	if(LIBPULSE_FOUND)
-		target_compile_definitions(${PROJECT_NAME} PRIVATE USE_PULSEAUDIO)
-		target_link_libraries(${PROJECT_NAME} PRIVATE PkgConfig::LIBPULSE)
+	if(USE_PULSEAUDIO)
+		pkg_check_modules(LIBPULSE IMPORTED_TARGET libpulse)
+		if(LIBPULSE_FOUND)
+			target_compile_definitions(${PROJECT_NAME} PRIVATE USE_PULSEAUDIO)
+			target_link_libraries(${PROJECT_NAME} PRIVATE PkgConfig::LIBPULSE)
+		endif()
 	endif()
 
 	if(USE_HOST_LIBZIP)