cmake: add swift test

cmake/test/main.swift

@@ -0,0 +1,13 @@
+/* Contributed by Piotr Usewicz (https://github.com/pusewicz) */
+
+import SDL3
+
+guard SDL_Init(Uint32(SDL_INIT_VIDEO)) == 0 else {
+  fatalError("SDL_Init error: \(String(cString: SDL_GetError()))")
+}
+
+var sdlVersion = SDL_GetVersion()
+
+print("SDL version: \(sdlVersion)")
+
+SDL_Quit()