[PATCH] add smp_read_barrier_depends() for m68knommu

This patch adds a definition for smp_read_barrier_depends() for the
m68knommu architecture. This is now needed to compile net/ipv4/route.c.

include/asm-m68knommu/system.h

@@ -102,10 +102,12 @@ asmlinkage void resume(void);
 #define smp_mb()	mb()
 #define smp_rmb()	rmb()
 #define smp_wmb()	wmb()
+#define smp_read_barrier_depends()	read_barrier_depends()
 #else
 #define smp_mb()	barrier()
 #define smp_rmb()	barrier()
 #define smp_wmb()	barrier()
+#define smp_read_barrier_depends()	do { } while(0)
 #endif
 
 #define xchg(ptr,x) ((__typeof__(*(ptr)))__xchg((unsigned long)(x),(ptr),sizeof(*(ptr))))