genirq: Add stub for set_handle_irq() when !GENERIC_IRQ_MULTI_HANDLER

In order to avoid compilation errors when a driver references set_handle_irq(),
but that the architecture doesn't select GENERIC_IRQ_MULTI_HANDLER,
add a stub function that will just WARN_ON_ONCE() if ever used.
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
[maz: commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200924071754.4509-2-thunder.leizhen@huawei.com

include/linux/irq.h

@@ -1252,6 +1252,12 @@ int __init set_handle_irq(void (*handle_irq)(struct pt_regs *));
  * top-level IRQ handler.
  */
 extern void (*handle_arch_irq)(struct pt_regs *) __ro_after_init;
+#else
+#define set_handle_irq(handle_irq)		\
+	do {					\
+		(void)handle_irq;		\
+		WARN_ON(1);			\
+	} while (0)
 #endif
 
 #endif /* _LINUX_IRQ_H */