demos/gtk-demo/listview*.c: Include stdlib.h

atoi() and qsort() both require this header for them to be defined

demos/gtk-demo/listview_colors.c

@@ -11,6 +11,8 @@
 
 #include <gtk/gtk.h>
 
+#include <stdlib.h>
+
 #define GTK_TYPE_COLOR (gtk_color_get_type ())
 G_DECLARE_FINAL_TYPE (GtkColor, gtk_color, GTK, COLOR, GObject)
 

demos/gtk-demo/listview_settings.c

@@ -9,6 +9,8 @@
 
 #include <gtk/gtk.h>
 
+#include <stdlib.h>
+
 /* Create an object that wraps GSettingsSchemaKey because that's a boxed type */
 typedef struct _SettingsKey SettingsKey;
 struct _SettingsKey