Create a build_config header file.

src/include/portability_sockets.h

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef NATIVE_CLIENT_SRC_INCLUDE_PORTABILITY_SOCKETS_H_
 #define NATIVE_CLIENT_SRC_INCLUDE_PORTABILITY_SOCKETS_H_ 1
 
+#include "native_client/src/include/nacl_defines.h"
+
 #if NACL_WINDOWS
 # include <winsock2.h>
 # include <windows.h>
 
 typedef SOCKET NaClSocketHandle;
 
 # define NaClCloseSocket closesocket
 # define NACL_INVALID_SOCKET INVALID_SOCKET
 # define NaClSocketGetLastError() WSAGetLastError()
 #else
 
 # include <arpa/inet.h>
 # include <netdb.h>
 # include <netinet/tcp.h>
 # include <sys/select.h>
 # include <sys/socket.h>
 
 typedef int NaClSocketHandle;
 
 # define NaClCloseSocket close
 # define NACL_INVALID_SOCKET (-1)
 # define NaClSocketGetLastError() errno
 
 #endif
 
 #endif  // NATIVE_CLIENT_SRC_INCLUDE_PORTABILITY_SOCKETS_H_