[d8] cleanly force exit in d8 on windows.

src/d8-posix.cc

Index: src/d8-posix.cc
diff --git a/src/d8-posix.cc b/src/d8-posix.cc
index d2cf573d4c013207b62d0b35d4e68e89c24cb4bd..cdfc39cc5de77e02880fc3bced34b13f811ab867 100644
--- a/src/d8-posix.cc
+++ b/src/d8-posix.cc
@@ -772,4 +772,12 @@ void Shell::AddOSMethods(Isolate* isolate, Local<ObjectTemplate> os_templ) {
                 FunctionTemplate::New(isolate, RemoveDirectory));
 }
 
+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);
+}
+
 }  // namespace v8