[MIPS] Update SConstruct to use new MIPS toolchain.

src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c

Index: src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
diff --git a/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c b/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
index fc750fe4a20aabc823867d8569dfe04387e8d87d..5aabbedc1ccbf070514acf6eedd55613eddeaf56 100644
--- a/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
+++ b/src/trusted/service_runtime/arch/mips/nacl_switch_to_app_mips.c
@@ -24,12 +24,10 @@ void NaClInitSwitchToApp(struct NaClApp *nap) {
 
 NORETURN void NaClStartThreadInApp(struct NaClAppThread *natp,
                                    uint32_t             new_prog_ctr) {
-  struct NaClApp  *nap;
   struct NaClThreadContext  *context;
 
   natp->user.trusted_stack_ptr = (NaClGetStackPtr() & ~0xf) + 4;
 
-  nap = natp->nap;
   context = &natp->user;
   context->new_prog_ctr = new_prog_ctr;