[PATCH] Make spinlock debugging compile on x86-64

cpu_relax is on i386 and x86-64 in processor.h, not system.h
This makes CONFIG_DEBUG_SPINLOCK compile for x86-64

include/linux/spinlock.h

@@ -13,6 +13,7 @@
 #include <linux/kernel.h>
 #include <linux/stringify.h>
 
+#include <asm/processor.h>	/* for cpu relax */
 #include <asm/system.h>
 
 /*