solarisaio: support signal driven async IO

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 25318ae..9d80237 100644
--- a/fio.h
+++ b/fio.h
@@ -164,6 +164,7 @@
 	union {
 		unsigned int index;
 		unsigned int seen;
+		void *engine_data;
 	};
 
 	unsigned int flags;