You could use external interrupt logic chip...
It raises an interrupt and then your interrupt routine will communicate to the logic chip to see wich interrupt was activated.
As you can see on this link it has an output E0 wich is low when none of the inputs are activated. If one or more of the inputs become activated, EO will become high, this line can be used to trigger your µC interrupt pin.
The 74148 will then encode the priority level of the interrupt into outputs A, B and C. So you can use these signals to see wich interrupt was activated.