powerpc/irq: use IS_ENABLED() in check_stack_overflow()

Instead of #ifdef, use IS_ENABLED(CONFIG_DEBUG_STACKOVERFLOW).
This enable GCC to check for code validity even when the option
is not selected.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200220115141.2707-4-mpe@ellerman.id.au

arch/powerpc/kernel/irq.c

@@ -599,9 +599,11 @@ u64 arch_irq_stat_cpu(unsigned int cpu)
 
 static inline void check_stack_overflow(void)
 {
-#ifdef CONFIG_DEBUG_STACKOVERFLOW
 	long sp;
 
+	if (!IS_ENABLED(CONFIG_DEBUG_STACKOVERFLOW))
+		return;
+
 	sp = current_stack_pointer & (THREAD_SIZE - 1);
 
 	/* check for stack overflow: is there less than 2KB free? */
@@ -609,7 +611,6 @@ static inline void check_stack_overflow(void)
 		pr_err("do_IRQ: stack overflow: %ld\n", sp);
 		dump_stack();
 	}
-#endif
 }
 
 void __do_irq(struct pt_regs *regs)