[MIPS] Make $t8 point to the address of TLS pointers

tests/thread_capture/arch/mips/thread_capture_test_injection.c

 /*
  * Copyright (c) 2013 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.
  */
 
 #include "native_client/tests/thread_capture/thread_capture_test_injection.h"
 
 #include "native_client/src/trusted/service_runtime/include/bits/nacl_syscalls.h"
 #include "native_client/src/trusted/service_runtime/nacl_app_thread.h"
 #include "native_client/src/trusted/service_runtime/nacl_copy.h"
 #include "native_client/src/trusted/service_runtime/nacl_syscall_register.h"
 #include "native_client/src/trusted/service_runtime/nacl_tls.h"
 
 static int32_t TestSyscall(struct NaClAppThread *natp) {
   UNREFERENCED_PARAMETER(natp);
 
   g_nacl_syscall_thread_capture_fault_addr =
       (uintptr_t) &NaClSyscallThreadCaptureFault;
 
-  NaClTlsSetCurrentThread(NULL);
+  natp->user.guard_token++;
 
   return 0;
 }
 
 NACL_DEFINE_SYSCALL_0(TestSyscall)
 
 void NaClInjectThreadCaptureSyscall(struct NaClApp *nap) {
   NACL_REGISTER_SYSCALL(nap, TestSyscall, NACL_sys_test_syscall_1);
 }