CMake: Do not autoselect between SDL3,2,1 anymore

CMakeLists.txt

@@ -564,7 +564,7 @@ elseif(NINTENDO_WIIU)
 elseif(AMIGA)
 	set(PLAYER_TARGET_PLATFORM "SDL1" CACHE STRING "Platform to compile for.")
 else()
-	set(PLAYER_TARGET_PLATFORM "SDL3" CACHE STRING "Platform to compile for. Options: SDL3 SDL2 SDL1 libretro")
+	set(PLAYER_TARGET_PLATFORM "Unset" CACHE STRING "Platform to compile for. Options: SDL3 SDL2 SDL1 libretro")
 	set_property(CACHE PLAYER_TARGET_PLATFORM PROPERTY STRINGS SDL3 SDL2 SDL1 libretro)
 endif()
 set(PLAYER_BUILD_EXECUTABLE ON)
@@ -579,7 +579,10 @@ if(ANDROID AND PLAYER_GRADLE_BUILD)
 	endforeach(f)
 endif()
 
-if(${PLAYER_TARGET_PLATFORM} STREQUAL "SDL3")
+if(${PLAYER_TARGET_PLATFORM} STREQUAL "Unset")
+	get_property(PLAT_PROP CACHE PLAYER_TARGET_PLATFORM PROPERTY STRINGS)
+	message(FATAL_ERROR "Please specify the target platform with -DPLAYER_TARGET_PLATFORM.\nOptions: ${PLAT_PROP}")
+elseif(${PLAYER_TARGET_PLATFORM} STREQUAL "SDL3")
 	target_sources(${PROJECT_NAME} PRIVATE
 		src/platform/sdl/sdl3_ui.cpp
 		src/platform/sdl/sdl3_ui.h)
@@ -714,9 +717,7 @@ else()
 endif()
 
 # Sound system to use
-if(PLAYER_AUDIO_BACKEND)
-	# already set earlier in the platform config
-elseif(${PLAYER_TARGET_PLATFORM} STREQUAL "SDL3")
+if(${PLAYER_TARGET_PLATFORM} STREQUAL "SDL3")
 	set(PLAYER_AUDIO_BACKEND "SDL3" CACHE STRING "Audio system to use. Options: SDL3 OFF")
 	set_property(CACHE PLAYER_AUDIO_BACKEND PROPERTY STRINGS SDL3 OFF)
 elseif(${PLAYER_TARGET_PLATFORM} STREQUAL "SDL2")
@@ -735,6 +736,7 @@ else()
 	set_property(CACHE PLAYER_AUDIO_BACKEND PROPERTY STRINGS ${PLAYER_TARGET_PLATFORM} OFF)
 endif()
 
+get_property(AUDIO_PROP CACHE PLAYER_AUDIO_BACKEND PROPERTY STRINGS)
 set(PLAYER_HAS_AUDIO ON)
 if(${PLAYER_AUDIO_BACKEND} STREQUAL "SDL3")
 	target_sources(${PROJECT_NAME} PRIVATE
@@ -758,7 +760,11 @@ elseif(${PLAYER_AUDIO_BACKEND} STREQUAL ${PLAYER_TARGET_PLATFORM})
 elseif(${PLAYER_AUDIO_BACKEND} STREQUAL "OFF")
 	set(PLAYER_HAS_AUDIO OFF)
 else()
-	message(FATAL_ERROR "Invalid Audio Backend ${PLAYER_AUDIO_BACKEND}")
+	message(FATAL_ERROR "Invalid Audio Backend ${PLAYER_AUDIO_BACKEND}\nOptions: ${AUDIO_PROP}")
+endif()
+
+if(NOT PLAYER_AUDIO_BACKEND IN_LIST AUDIO_PROP)
+	message(FATAL_ERROR "Incompatible audio backend configuration ${PLAYER_AUDIO_BACKEND}.\nPlease clear the CMake cache.\nOptions: ${AUDIO_PROP}")
 endif()
 
 # Shared by homebrew platforms