Non-transient dialog with minimize button (which doesn't work)

sample.c

/* 
 * Build:
 * gcc $(pkg-config --cflags gtk+-3.0) sample.c -o sample $(pkg-config --libs gtk+-3.0)
 */

#include <gtk/gtk.h>

int main (int argc, char *argv[])
{
  GtkWidget *window, *dialog;

  gtk_init (&argc, &argv);

  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);

  gtk_window_set_position (GTK_WINDOW (window), GTK_WIN_POS_CENTER);
  gtk_window_set_default_size (GTK_WINDOW (window), 640, 480);

  dialog = gtk_window_new (GTK_WINDOW_TOPLEVEL);

  gtk_window_set_position (GTK_WINDOW (dialog), GTK_WIN_POS_CENTER);
  gtk_window_set_default_size (GTK_WINDOW (dialog), 320, 240);
  gtk_window_set_type_hint (GTK_WINDOW (dialog), GDK_WINDOW_TYPE_HINT_DIALOG);
  // gtk_window_set_transient_for (GTK_WINDOW (dialog), GTK_WINDOW (window));

  g_signal_connect (G_OBJECT (window), "destroy", G_CALLBACK (gtk_main_quit), NULL);

  gtk_widget_show_all (window);
  gtk_widget_show_all (dialog);

  gtk_main ();

  return 0;
}