[MIPS] Do not use pnacl-irt-link for MIPS target.

SConstruct

 #! -*- python -*-
 # Copyright (c) 2012 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.
 
 import atexit
 import os
 import platform
 import re
 import subprocess
@@ skipping 3104 matching lines @@
     nacl_irt_env.Append(CCFLAGS=['--pnacl-frontend-triple=i686-unknown-nacl'])
   elif nacl_irt_env.Bit('target_x86_64'):
     nacl_irt_env.Append(CCFLAGS=['--pnacl-frontend-triple=x86_64-unknown-nacl'])
 
 
 # All IRT code must avoid direct use of the TLS ABI register, which
 # is reserved for user TLS.  Instead, ensure all TLS accesses use a
 # call to __nacl_read_tp, which the IRT code overrides to segregate
 # IRT-private TLS from user TLS.
 if nacl_irt_env.Bit('bitcode'):
-  nacl_irt_env.Append(LINKFLAGS=['--pnacl-allow-native',
-                                 '-Wt,-mtls-use-call',
-                                 '-Wl,--pnacl-irt-link'])
+  nacl_irt_env.Append(LINKFLAGS=['--pnacl-allow-native', '-Wt,-mtls-use-call'])
+  if nacl_irt_env.Bit('target_arm'):
+    nacl_irt_env.Append(LINKFLAGS=['-Wl,--pnacl-irt-link'])
 elif nacl_irt_env.Bit('target_arm'):
   nacl_irt_env.Append(CCFLAGS=['-mtp=soft'])
 else:
   nacl_irt_env.Append(CCFLAGS=['-mtls-use-call'])
 # A debugger should be able to unwind IRT call frames. As the IRT is compiled
 # with high level of optimizations and without debug info, compiler is requested
 # to generate unwind tables explicitly. This is the default behavior on x86-64
 # and when compiling C++ with exceptions enabled, the change is for the benefit
 # of x86-32 C.
 # TODO(eaeltsin): enable unwind tables for ARM
@@ skipping 380 matching lines @@
   nacl_env.ValidateSdk()
 
 if BROKEN_TEST_COUNT > 0:
   msg = "There are %d broken tests." % BROKEN_TEST_COUNT
   if GetOption('brief_comstr'):
     msg += " Add --verbose to the command line for more information."
   print msg
 
 # separate warnings from actual build output
 Banner('B U I L D - O U T P U T:')