checkkeysthreads: Create a renderer for window display on Wayland

Applies checkkeys patch from 105f1206 to checkkeysthreads.

test/checkkeysthreads.c

@@ -224,6 +224,7 @@ int
 main(int argc, char *argv[])
 {
     SDL_Window *window;
+    SDL_Renderer *renderer;
     SDL_Thread *thread;
 
     /* Enable standard application logging */
@@ -245,6 +246,12 @@ main(int argc, char *argv[])
         quit(2);
     }
 
+    /* On wayland, no window will actually show until something has
+       actually been displayed.
+    */
+    renderer = SDL_CreateRenderer(window, -1, 0);
+    SDL_RenderPresent(renderer);
+
 #if __IPHONEOS__
     /* Creating the context creates the view, which we need to show keyboard */
     SDL_GL_CreateContext(window);