[NaCl SDK] Re-land "Added support for NaCl IO to use the IRT Extension API."

native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc

 // Copyright (c) 2012 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.
 
 #include <sys/types.h>  // Include something that will define __GLIBC__.
+#include "nacl_io/kernel_wrap.h" // IRT_EXT is turned on in this header.
 
-// The entire file is wrapped in this #if. We do this so this .cc file can be
-// compiled, even on a non-glibc build.
-// The ARM glibc toolchain uses a different IRT hooks mechanism and is not
-// yet supported by nacl_io.
-#if defined(__native_client__) && defined(__GLIBC__) && !defined(__arm__)
-
-#include "nacl_io/kernel_wrap.h"
+#if !defined(NACL_IO_IRT_EXT) && defined(__native_client__) && \
+    defined(__GLIBC__)
 
 #include <alloca.h>
 #include <assert.h>
 #include <dirent.h>
 #include <errno.h>
 #include <irt.h>
 #include <irt_syscalls.h>
 #include <nacl_stat.h>
 #include <string.h>
 #include <sys/stat.h>
@@ skipping 639 matching lines @@
   if (s_wrapped) {
     LOG_TRACE("kernel_wrap_uninit");
     EXPAND_SYMBOL_LIST_OPERATION(USE_REAL)
     s_wrapped = false;
   }
 }
 
 EXTERN_C_END
 
 #endif  // defined(__native_client__) && defined(__GLIBC__)