Fix missing #includes in system/core.

Change-Id: I4736e8c4f7bb8bb03640d26d58243efaa67dc75c
diff --git a/fastbootd/transport.c b/fastbootd/transport.c
index 9a16fd7..232c999 100644
--- a/fastbootd/transport.c
+++ b/fastbootd/transport.c
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <errno.h>
 #include <pthread.h>
 #include <stddef.h>
 #include <stdio.h>