[builtins] Fix context for ConstructStub calls into C++.

src/ppc/builtins-ppc.cc

Index: src/ppc/builtins-ppc.cc
diff --git a/src/ppc/builtins-ppc.cc b/src/ppc/builtins-ppc.cc
index b1a8a83c69f8af2e13d4f56e28b5eae9ee395b03..c431fc18682ce008a5250f5cb243b7de016d24c3 100644
--- a/src/ppc/builtins-ppc.cc
+++ b/src/ppc/builtins-ppc.cc
@@ -30,6 +30,12 @@ void Builtins::Generate_Adaptor(MacroAssembler* masm, CFunctionId id,
   // -----------------------------------
   __ AssertFunction(r4);
 
+  // Make sure we operate in the context of the called function (for example
+  // ConstructStubs implemented in C++ will be run in the context of the caller
+  // instead of the callee, due to the way that [[Construct]] is defined for
+  // ordinary functions).
+  __ LoadP(cp, FieldMemOperand(r4, JSFunction::kContextOffset));
+
   // Insert extra arguments.
   int num_extra_args = 0;
   switch (extra_args) {