Following changes introduced in bpo-15002, HTTPError closes its fp when GCed via tempfile._TemporaryFileCloser's finalizer. However, the current implementation of _TemporaryFileCloser only defines __del__ for non-NT platforms.

Assuming HTTPError.fp is part of the API (though it's currently undocumented), and assuming the desired behaviour is to close fp when HTTPError is finalized, then perhaps _TemporaryFileCloser should always define __del__?

A contrived example follows:

```
from urllib.error import HTTPError
from urllib.request import urlopen

def make_request():
    try:
        urlopen('https://httpbin.org/status/418')
        assert False
    except HTTPError as err:
        assert err.code == 418
        return err.fp

fp = make_request()
assert fp.isclosed()  # Fails on Windows, passes on other platforms
```