Stat: treat pending deletes as missing files on Windows

Stat: treat pending deletes as missing files on Windows

Win32 functions like `CreateFile` return `ERROR_ACCESS_DENIED` when a
file is in the process of being deleted, which gets mapped to an errno
of `EACCES`. For the purposes of `Stat::stat` and `Stat::lstat`, it's
more useful to treat this as a missing file and mapping this to an errno
of `ENOENT`.