tools/virtio: stub out strong barriers

The tool should never use them, abort if it does.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/linux/virtio.h

@@ -181,6 +181,9 @@ struct virtqueue {
 #define smp_mb()	mb()
 # define smp_rmb()	barrier()
 # define smp_wmb()	barrier()
+/* Weak barriers should be used. If not - it's a bug */
+# define rmb()	abort()
+# define wmb()	abort()
 #else
 #error Please fill in barrier macros
 #endif