Sets the comparison function used when sorting to be sort_func.
If the current sort column id of this is the same as sort_column_id, then the model will
sort using this function.
| this |
A `GtkTreeSortable` |
| sort_column_id |
the sort column id to set the function for |
| sort_func |
The comparison function |
| destroy |
Destroy notifier of |
| user_data |
User data to pass to |