x/sys/windows: add missing file attributes

[Kropekk]

In syscall library for Windows (version for amd64 architecture ) not all file attributes are present.

There are some constants already defined (FILE_ATTRIBUTE_*), but I would expect to see all of them or at least all applicable to syscall.SetFileAttributes(...) function (msdn docs for underlying function).

On the other hand, the remaining ones would be helpful in parsing syscall.GetFileAttributes(...) return value.

Summing up, I think that all FILE_ATTRIBUTE_* constants should be present in Windows-OS syscall library.

(BTW, I wanted to attach some labels to my issue, but I think it's not possible for a newcomer)

[ianlancetaylor]

We aren't going to add any more constants to the syscall package. They should be added to the golang.org/x/sys/windows package instead. See https://docs.google.com/document/d/1QXzI9I1pOfZPujQzxhyRy6EeHYTQitKKjHfpq0zpxZs/edit#heading=h.5nqylt8x3hka .

[gopherbot]

Change https://golang.org/cl/122236 mentions this issue: windows: add missing file attributes