demos: add some fflushes for windows

progs/demos/gearbox.c

@@ -314,6 +314,7 @@ draw(void)
          GLfloat seconds = (t - T0) / 1000.0;
          GLfloat fps = Frames / seconds;
          printf("%d frames in %6.3f seconds = %6.3f FPS\n", Frames, seconds, fps);
+         fflush(stdout);
          T0 = t;
          Frames = 0;
       }