[PATCH] percpu: fix compile warning for UP builds

A typical construct is:

	int cpu = get_cpu();

	foo = per_cpu(bar, cpu);
	put_cpu();

but this generates a compiler warning on uniprocessor builds: unused
variable `cpu'.

Add a dummy ref to `cpu' to per_cpu() to prevent this.

include/asm-generic/percpu.h

@@ -25,7 +25,7 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
     __typeof__(type) name##__per_cpu
 #endif
 
-#define per_cpu(var, cpu)			var##__per_cpu
+#define per_cpu(var, cpu)			((void)cpu, var##__per_cpu)
 #define __get_cpu_var(var)			var##__per_cpu
 #endif
 

include/asm-ia64/percpu.h

@@ -29,7 +29,7 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
 #ifdef CONFIG_SMP
 # define per_cpu(var, cpu)	(*RELOC_HIDE(&var##__per_cpu, __per_cpu_offset[cpu]))
 #else
-# define per_cpu(var, cpu)	__get_cpu_var(var)
+# define per_cpu(var, cpu)	((void)cpu, __get_cpu_var(var))
 #endif
 
 #endif /* !__ASSEMBLY__ */

include/asm-x86_64/percpu.h

@@ -34,7 +34,7 @@ extern unsigned long __per_cpu_offset[NR_CPUS];
     __typeof__(type) name##__per_cpu
 #endif
 
-#define per_cpu(var, cpu)			var##__per_cpu
+#define per_cpu(var, cpu)			((void)cpu, var##__per_cpu)
 #define __get_cpu_var(var)			var##__per_cpu
 #endif