emsdk install very old SDL2 headers

SDK Version : 2.0.25
hash : 'sdk-releases-upstream-f6f001b08fbb67935379cf13d17fd9bfdbaff791-64bit'
OS : Ubuntu 20 under WSL2

I tried to use SDL_FRect, but in upstream's include/SDL/SDL_Rect.h, there is no SDL_FRect.

I found that Copyright of header file is very old.

```
Simple DirectMedia Layer
Copyright (C) 1997-2011 Sam Lantinga
```

I have no idea why emsdk install the old sdl2.

How can emsdk install newer SDL2?