[NaCl SDK] Get nacl_mounts_tests building.

native_client_sdk/src/libraries/gtest/nacl_gtest_dummy_sys.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.
+
+#if defined(__native_client__)
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
+#endif
+
+extern "C" {
+
+#if defined(__native_client__)
+
+char* getcwd(char* buf, size_t size) {
+  if (size < 2) {
+    errno = ERANGE;
+    return NULL;
+  }
+
+  return strncpy(buf, ".", size);
+}
+
+int unlink(const char* pathname) {
+  errno = ENOSYS;
+  return -1;
+}
+
+int mkdir(const char* pathname, mode_t mode) {
+  errno = ENOSYS;
+  return -1;
+}
+
+#endif
+
+}  // extern "C"