[MIPS] Restore the trusted stack in NaClSyscallSeg.

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

Index: src/trusted/service_runtime/arch/mips/sel_rt.c
diff --git a/src/trusted/service_runtime/arch/mips/sel_rt.c b/src/trusted/service_runtime/arch/mips/sel_rt.c
index 37e0d7e68eb46e79c57e08746e9b5102a5c4a69d..37171e3070e09a740905a99e3fddb4953e1ee9a2 100644
--- a/src/trusted/service_runtime/arch/mips/sel_rt.c
+++ b/src/trusted/service_runtime/arch/mips/sel_rt.c
@@ -90,7 +90,7 @@ void NaClThreadContextToSignalContext(const struct NaClThreadContext *th_ctx,
   sig_ctx->t9          = 0;
   sig_ctx->k0          = 0;
   sig_ctx->k1          = 0;
-  sig_ctx->global_ptr  = th_ctx->global_ptr;
+  sig_ctx->global_ptr  = 0;
   sig_ctx->stack_ptr   = th_ctx->stack_ptr;
   sig_ctx->frame_ptr   = th_ctx->frame_ptr;
   sig_ctx->return_addr = th_ctx->prog_ctr;