tools/virtio: add barrier for aarch64

Add barrier for aarch64 for cross compiling, and most are from Linux Kernel.

Signed-off-by: Peng Fan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Michael S. Tsirkin <[e-mail]>

tools/virtio/asm/barrier.h

···
 # define mb() abort()
 # define dma_rmb() abort()
 # define dma_wmb() abort()
+#elif defined(__aarch64__)
+#define dmb(opt) asm volatile("dmb " #opt : : : "memory")
+#define virt_mb() __sync_synchronize()
+#define virt_rmb() dmb(ishld)
+#define virt_wmb() dmb(ishst)
+#define virt_store_mb(var, value)  do { WRITE_ONCE(var, value); dmb(ish); } while (0)
+/* Weak barriers should be used. If not - it's a bug */
+# define mb() abort()
+# define dma_rmb() abort()
+# define dma_wmb() abort()
 #else
 #error Please fill in barrier macros
 #endif