Kernel: Add Interrupts/IRQHandler.cpp to the aarch64 build

This requires a few stubs such that the compiler won't complain.

Kernel/Arch/aarch64/Dummy.cpp

@@ -146,4 +146,14 @@ u8 InterruptManagement::acquire_mapped_interrupt_number(u8)
     VERIFY_NOT_REACHED();
 }
 
+InterruptManagement& InterruptManagement::the()
+{
+    VERIFY_NOT_REACHED();
+}
+
+RefPtr<IRQController> InterruptManagement::get_responsible_irq_controller(u8)
+{
+    VERIFY_NOT_REACHED();
+}
+
 }

Kernel/CMakeLists.txt

@@ -452,6 +452,7 @@ else()
         Memory/VMObject.cpp
 
         Interrupts/GenericInterruptHandler.cpp
+        Interrupts/IRQHandler.cpp
     )
 
     # Otherwise linker errors e.g undefined reference to `__aarch64_cas8_acq_rel'