Sets @label_widget as the widget that will be used as the label
for @button. If @label_widget is %NULL the #GtkToolButton:label property is used
as label. If #GtkToolButton:label is also %NULL, the label in the stock item
determined by the #GtkToolButton:stock-id property is used as label. If
#GtkToolButton:stock-id is also %NULL, @button does not have a label.
Sets @label_widget as the widget that will be used as the label for @button. If @label_widget is %NULL the #GtkToolButton:label property is used as label. If #GtkToolButton:label is also %NULL, the label in the stock item determined by the #GtkToolButton:stock-id property is used as label. If #GtkToolButton:stock-id is also %NULL, @button does not have a label.