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

native_client_sdk/src/tests/nacl_io_test/kernel_wrap_test.cc

 // 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.
 
+// The linux host build of nacl_io can't do wrapping of syscalls so all
+// these tests must be disabled.
+#if !defined(__linux__)
+
 #include <unistd.h>
 
 #include <string>
 #include <vector>
 
 #include "gtest/gtest.h"
 #include "kernel_proxy_mock.h"
 #include "nacl_io/kernel_intercept.h"
 #include "nacl_io/kernel_wrap.h"
 #include "nacl_io/osmman.h"
@@ skipping 692 matching lines @@
 
 TEST_F(KernelWrapTest, socketpair) {
   int dummy_val;
   EXPECT_CALL(mock, socketpair(kDummyInt, kDummyInt2, kDummyInt3, &dummy_val))
       .WillOnce(Return(kDummyInt4));
   EXPECT_EQ(kDummyInt4,
             socketpair(kDummyInt, kDummyInt2, kDummyInt3, &dummy_val));
 }
 
 #endif  // PROVIDES_SOCKET_API
+
+#endif  // __linux__