remove sdl subtree and update

external/sdl/CMakeLists.txt

@@ -1,9 +1,17 @@
-cmake_minimum_required(VERSION 3.9 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.16...3.24 FATAL_ERROR)
 
-set(SDL_SHARED OFF CACHE INTERNAL "")
-set(SDL_STATIC ON CACHE INTERNAL "")
-#TODO: pic ?
+include(FetchContent)
 
-add_subdirectory(./SDL EXCLUDE_FROM_ALL)
-#add_subdirectory(./SDL)
+if (NOT TARGET SDL3::SDL3)
+	set(SDL_SHARED OFF CACHE INTERNAL "")
+	set(SDL_STATIC ON CACHE INTERNAL "")
+	#TODO: pic ?
+
+	FetchContent_Declare(SDL3
+		GIT_REPOSITORY https://github.com/libsdl-org/SDL
+		GIT_TAG 0429f5d6a36fc35b551bcc2acd4a40c2db6dab82 # tip when looking
+		FIND_PACKAGE_ARGS # for the future
+	)
+	FetchContent_MakeAvailable(SDL3)
+endif()