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

SConstruct

Index: SConstruct
diff --git a/SConstruct b/SConstruct
index f1ecbbed7d75053581579d28e07447e30b1564eb..f647d3d25cb0f75074f17f0ce0e14d1107c4c539 100755
--- a/SConstruct
+++ b/SConstruct
@@ -3122,9 +3122,9 @@ if nacl_irt_env.Bit('bitcode'):
 # 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: