[d8] cleanly force exit in d8 on windows.

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 66e3b518a50933adc4d8dad2aea99ac6a130727a..4b156b22c651a9e71250a3f58192701d951aa218 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -1569,16 +1569,6 @@ Local<Context> Shell::CreateEvaluationContext(Isolate* isolate) {
   return handle_scope.Escape(context);
 }
 
-
-void Shell::Exit(int exit_code) {
-  // Use _exit instead of exit to avoid races between isolate
-  // threads and static destructors.
-  fflush(stdout);
-  fflush(stderr);
-  _exit(exit_code);
-}
-
-
 struct CounterAndKey {
   Counter* counter;
   const char* key;