[torch package] Treat builtins as default extern module (#88385)
Summary: When using torch deploy, if we do fx transformation and then try to pickle/unpickle a fx GraphModule, it's possible that the GraphModule's code depends on `builtins` but we didn't add it to extern module.
Reviewed By: PaliC
Differential Revision: D40958730
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88385
Approved by: https://github.com/PaliC
