Adds missing include <cerrno>

Include ordering in other files must have been making this work before,
but it broke for me when I included this file first.

Change-Id: I1203ee38974dbbebed6aca80ddbbc22925f0053a
diff --git a/common/vsoc/lib/circqueue_impl.h b/common/vsoc/lib/circqueue_impl.h
index d40399b..10a78dd 100644
--- a/common/vsoc/lib/circqueue_impl.h
+++ b/common/vsoc/lib/circqueue_impl.h
@@ -16,6 +16,7 @@
  * limitations under the License.
  */
 
+#include <cerrno>
 #include <string.h>
 
 #include "common/vsoc/lib/region_signaling_interface.h"