Changes to LLVM to support deoptimization.

Added a magic exception value (-1) and a handler to transition
to the interpreter. This is currently untested.

Change-Id: I2f53135e7505c54355ecf7c579897f68bbdcbda3
diff --git a/src/stack.h b/src/stack.h
index c3d20f5..18a2101 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -315,6 +315,10 @@
     return top_shadow_frame_;
   }
 
+  void SetTopShadowFrame(ShadowFrame* top) {
+    top_shadow_frame_ = top;
+  }
+
   static size_t TopShadowFrameOffset() {
     return OFFSETOF_MEMBER(ManagedStack, top_shadow_frame_);
   }