tools/virtio: fix build after 4.2 changes

more stubs, mostly
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

tools/virtio/asm/barrier.h

@@ -3,6 +3,8 @@
 #define mb() __sync_synchronize()
 
 #define smp_mb()	mb()
+# define dma_rmb()	barrier()
+# define dma_wmb()	barrier()
 # define smp_rmb()	barrier()
 # define smp_wmb()	barrier()
 /* Weak barriers should be used. If not - it's a bug */

tools/virtio/linux/export.h

+#define EXPORT_SYMBOL_GPL(sym) extern typeof(sym) sym
+#define EXPORT_SYMBOL(sym) extern typeof(sym) sym
+

tools/virtio/linux/kernel.h

@@ -22,6 +22,7 @@
 
 typedef unsigned long long dma_addr_t;
 typedef size_t __kernel_size_t;
+typedef unsigned int __wsum;
 
 struct page {
 	unsigned long long dummy;
@@ -47,6 +48,13 @@ static inline void *kmalloc(size_t s, gfp_t gfp)
 		return __kmalloc_fake;
 	return malloc(s);
 }
+static inline void *kzalloc(size_t s, gfp_t gfp)
+{
+	void *p = kmalloc(s, gfp);
+
+	memset(p, 0, s);
+	return p;
+}
 
 static inline void kfree(void *p)
 {