Always include <sys/cdefs.h> first.

Otherwise you can't be sure that things like __BIONIC__ work.

Change-Id: Ic5e59988b69419828c3b1a97332c7e2ab58e09a1
diff --git a/libc/include/netinet/in.h b/libc/include/netinet/in.h
index 163e614..d4ce302 100644
--- a/libc/include/netinet/in.h
+++ b/libc/include/netinet/in.h
@@ -28,9 +28,10 @@
 
 #pragma once
 
+#include <sys/cdefs.h>
+
 #include <endian.h>
 #include <netinet/in6.h>
-#include <sys/cdefs.h>
 #include <sys/socket.h>
 
 #include <linux/in.h>