PPC: Make Simulator respect C stack limits as well.

src/ppc/simulator-ppc.h

Index: src/ppc/simulator-ppc.h
diff --git a/src/ppc/simulator-ppc.h b/src/ppc/simulator-ppc.h
index fe655ff582cdb6eefd8c3efd4c214505f24f8563..042b2ada2c6edf51d9489870c36395cf52f0a81c 100644
--- a/src/ppc/simulator-ppc.h
+++ b/src/ppc/simulator-ppc.h
@@ -199,12 +199,12 @@ class Simulator {
   void set_pc(intptr_t value);
   intptr_t get_pc() const;
 
-  Address get_sp() {
+  Address get_sp() const {
     return reinterpret_cast<Address>(static_cast<intptr_t>(get_register(sp)));
   }
 
   // Accessor to the internal simulator stack area.
-  uintptr_t StackLimit() const;
+  uintptr_t StackLimit(uintptr_t c_limit) const;
 
   // Executes PPC instructions until the PC reaches end_sim_pc.
   void Execute();
@@ -403,15 +403,14 @@ class Simulator {
 
 
 // The simulator has its own stack. Thus it has a different stack limit from
-// the C-based native code.  Setting the c_limit to indicate a very small
-// stack cause stack overflow errors, since the simulator ignores the input.
-// This is unlikely to be an issue in practice, though it might cause testing
-// trouble down the line.
+// the C-based native code.  The JS-based limit normally points near the end of
+// the simulator stack.  When the C-based limit is exhausted we reflect that by
+// lowering the JS-based limit as well, to make stack checks trigger.
 class SimulatorStack : public v8::internal::AllStatic {
  public:
   static inline uintptr_t JsLimitFromCLimit(v8::internal::Isolate* isolate,
                                             uintptr_t c_limit) {
-    return Simulator::current(isolate)->StackLimit();
+    return Simulator::current(isolate)->StackLimit(c_limit);
   }
 
   static inline uintptr_t RegisterCTryCatch(uintptr_t try_catch_address) {