Fixed compiling test with older C.

test/relative_mode.markdown

@@ -37,9 +37,11 @@ Code
 
     int main(int argc, char *argv[])
     {
+        SDL_Window *win;
+
         SDL_Init(SDL_INIT_VIDEO);
 
-        SDL_Window *win = SDL_CreateWindow("Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 800, 600, 0);
+        win = SDL_CreateWindow("Test", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 800, 600, 0);
         SDL_SetRelativeMouseMode(SDL_TRUE);
 
         while (1)