Update SDL2 to version 2.28.1.

libs/SDL2/cmake/test/main_cli.c

@@ -0,0 +1,14 @@
+#define SDL_MAIN_HANDLED
+#include "SDL.h"
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+    SDL_SetMainReady();
+    if (SDL_Init(0) < 0) {
+        fprintf(stderr, "could not initialize sdl2: %s\n", SDL_GetError());
+        return 1;
+    }
+    SDL_Delay(100);
+    SDL_Quit();
+    return 0;
+}