Prevent clang from doing tail-call elimination in DartEntry::InvokeClosure.

TEST=language/issue21159_test.dart with --noopt
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Review URL: https://codereview.chromium.org/1587293002 .

Author: rmacnak-google

runtime/vm/dart_entry.cc

@@ -192,7 +192,12 @@ RawObject* DartEntry::InvokeClosure(const Array& arguments,
         ASSERT(getter_result.IsNull() || getter_result.IsInstance());
 
         arguments.SetAt(0, getter_result);
-        return InvokeClosure(arguments, arguments_descriptor);
+        // This otherwise unnecessary handle is used to prevent clang from
+        // doing tail call elimination, which would make the stack overflow
+        // check above ineffective.
+        Object& result = Object::Handle(InvokeClosure(arguments,
+                                                      arguments_descriptor));
+        return result.raw();
       }
       cls = cls.SuperClass();
     }