Always include <sys/cdefs.h>.

I made a mistake caught by code review earlier, so let's try to be
safer by default.

This patch also moves all our "forwarding" headers to the guardless
just-include-the-other-thing style that we usually use. (Where we
have a comment explaining where the header comes from, I've kept
that.)

Change-Id: I37342cf5e2563c6a269b2ba61a697069b1c7913b
diff --git a/libc/include/arpa/inet.h b/libc/include/arpa/inet.h
index e4f94ef..d137130 100644
--- a/libc/include/arpa/inet.h
+++ b/libc/include/arpa/inet.h
@@ -29,9 +29,10 @@
 #ifndef _ARPA_INET_H_
 #define _ARPA_INET_H_
 
-#include <stdint.h>
-#include <sys/types.h>
 #include <netinet/in.h>
+#include <stdint.h>
+#include <sys/cdefs.h>
+#include <sys/types.h>
 
 __BEGIN_DECLS
 
diff --git a/libc/include/arpa/nameser_compat.h b/libc/include/arpa/nameser_compat.h
index 539864e..6868876 100644
--- a/libc/include/arpa/nameser_compat.h
+++ b/libc/include/arpa/nameser_compat.h
@@ -40,9 +40,10 @@
 #ifndef _ARPA_NAMESER_COMPAT_
 #define	_ARPA_NAMESER_COMPAT_
 
-#define	__BIND		19950621	/* (DEAD) interface version stamp. */
-
 #include <endian.h>
+#include <sys/cdefs.h>
+
+#define	__BIND		19950621	/* (DEAD) interface version stamp. */
 
 /*
  * Structure for query header.  The order of the fields is machine- and
diff --git a/libc/include/arpa/telnet.h b/libc/include/arpa/telnet.h
index b8212f8..594dc7a 100644
--- a/libc/include/arpa/telnet.h
+++ b/libc/include/arpa/telnet.h
@@ -32,6 +32,8 @@
 #ifndef _ARPA_TELNET_H
 #define	_ARPA_TELNET_H 1
 
+#include <sys/cdefs.h>
+
 /*
  * Definitions for the TELNET protocol.
  */