ringtest: test build fix

Recent changes to ptr_ring broke the ringtest
which lacks a likely() stub. Fix it up.

Fixes: 982fb490
	("ptr_ring: support zero length ring")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/ringtest/ptr_ring.c

@@ -13,6 +13,7 @@
 #define cache_line_size() SMP_CACHE_BYTES
 #define ____cacheline_aligned_in_smp __attribute__ ((aligned (SMP_CACHE_BYTES)))
 #define unlikely(x)    (__builtin_expect(!!(x), 0))
+#define likely(x)    (__builtin_expect(!!(x), 1))
 #define ALIGN(x, a) (((x) + (a) - 1) / (a) * (a))
 typedef pthread_spinlock_t  spinlock_t;