[NaCl SDK] Enable linux host build for nacl_io and nacl_io_tests.

native_client_sdk/src/libraries/nacl_io/fifo_interface.h

 // Copyright (c) 2013 The Chromium 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 LIBRARIES_NACL_IO_FIFO_INTERFACE_H_
 #define LIBRARIES_NACL_IO_FIFO_INTERFACE_H_
 
 #include <stdint.h>
 #include <stdlib.h>
 
 namespace nacl_io {
 
 // FIFOInterface
 //
 // FIFOInterface provides a common interface for Emitters to update their
 // signalled state.  FIFOs do not have any internal locking and instead
 // reply on a parent (usually an emitter) to lock for them as appropriate.
 class FIFOInterface {
  public:
   virtual ~FIFOInterface() {};
 
   virtual bool IsEmpty() = 0;
   virtual bool IsFull() = 0;
   virtual bool Resize(size_t len) = 0;
 
-  virtual uint32_t ReadAvailable() = 0;
-  virtual uint32_t WriteAvailable() = 0;
+  virtual size_t ReadAvailable() = 0;
+  virtual size_t WriteAvailable() = 0;
 };
 
 }  // namespace nacl_io
 
 #endif  // LIBRARIES_NACL_IO_FIFO_INTERFACE_H_