change build system to CMake and use SDL3 for everything

libs/SDL3/cmake/test/main.swift

@@ -0,0 +1,13 @@
+/* Contributed by Piotr Usewicz (https://github.com/pusewicz) */
+
+import SDL3
+
+guard SDL_Init(SDL_INIT_VIDEO) else {
+  fatalError("SDL_Init error: \(String(cString: SDL_GetError()))")
+}
+
+var sdlVersion = SDL_GetVersion()
+
+print("SDL version: \(sdlVersion)")
+
+SDL_Quit()