cmake: Add mini-SDL2 CMake project to test SDL2 prefixes

cmake/test/main_gui.c

@@ -0,0 +1,28 @@
+#include "SDL.h"
+#include <stdio.h>
+
+int main(int argc, char *argv[]) {
+    SDL_Window *window = NULL;
+    SDL_Surface *screenSurface = NULL;
+    if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+        fprintf(stderr, "could not initialize sdl2: %s\n", SDL_GetError());
+        return 1;
+    }
+    window = SDL_CreateWindow(
+            "hello_sdl2",
+            SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED,
+            640, 480,
+            SDL_WINDOW_SHOWN
+    );
+    if (window == NULL) {
+        fprintf(stderr, "could not create window: %s\n", SDL_GetError());
+        return 1;
+    }
+    screenSurface = SDL_GetWindowSurface(window);
+    SDL_FillRect(screenSurface, NULL, SDL_MapRGB(screenSurface->format, 0xff, 0xff, 0xff));
+    SDL_UpdateWindowSurface(window);
+    SDL_Delay(100);
+    SDL_DestroyWindow(window);
+    SDL_Quit();
+    return 0;
+}