[PATCH for-4.{17,18}] evtchn: build fix for Arm

[Jan Beulich]

When backporting daa90dfea917 ("pirq_cleanup_check() leaks") I neglected
to pay attention to it depending on 13a7b0f9f747 ("restrict concept of
pIRQ to x86"). That one doesn't want backporting imo, so use / adjust
custom #ifdef-ary to address the immediate issue of pirq_cleanup_check()
not being available on Arm.

Signed-off-by: Jan Beulich <jbeul...@suse.com>
---
Sending here just for completeness; I don't think I'll be waiting for
any acks or alike.

--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -643,7 +643,9 @@
     if ( rc != 0 )
     {
         info->evtchn = 0;
+#ifdef CONFIG_X86
         pirq_cleanup_check(info, d);
+#endif
         goto out;
     }
 
@@ -713,8 +715,8 @@
                  * The successful path of unmap_domain_pirq_emuirq() will have
                  * called pirq_cleanup_check() already.
                  */
-#endif
                 pirq_cleanup_check(pirq, d1);
+#endif
         }
         unlink_pirq_port(chn1, d1->vcpu[chn1->notify_vcpu_id]);
         break;