GPIO inputs of most MCUs do have some hystheresis and more or less constant threshold levels, so you can connect voltage divider directly to the interrupt pin.
You may need a debounce procedure in software for proper operation (i.e. to avoid interrupt storm).
If you wish to have exact threshold, you can use voltage comparator. Some MCUs do have built in comparators.
Third option is ADC. It is usually slower and less reliable, but you will get a voltage value to play with.