Adds tls_edit utility which patches irt_core.nexe's TLS usage.

src/untrusted/irt/aeabi_read_tp.S

-/*
- * Copyright (c) 2011 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/src/trusted/service_runtime/nacl_config.h"
-
-/*
- * The IRT uses its own private TLS, leaving [r9, #0] for the
- * application.  We must define __aeabi_read_tp to get the private one
- * instead of the standard one.  The EABI requires that this function
- * preserve all registers except r0 (the return value register).  A
- * normal function is permitted to clobber r1, r2, and r3 as well.
- */
-
-        .globl __aeabi_read_tp
-        .type __aeabi_read_tp,%function
-        .p2align NACL_BLOCK_SHIFT
-__aeabi_read_tp:
-        ldr r0, [r9, #4]
-        bic lr, lr, #NACL_CONTROL_FLOW_MASK
-        bx lr