syscall: support O_SYNC flag for os.OpenFile on windows
os.OpenFile on windows did not use the O_SYNC flag. This meant
that even if the user set O_SYNC, os.OpenFile would ignore it.
This change adds a new flag FILE_FLAG_WRITE_THROUGH, which is
the equivalent of O_SYNC flag on Linux and is documented in
https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
Fixes #35358
Change-Id: Ib338caed5bb2f215723bfe30a2551a83998d92c9
GitHub-Last-Rev:
82c6275cb49602d7903b2bff7d60b7c772a5d91a
GitHub-Pull-Request: golang/go#64027
Reviewed-on: https://go-review.googlesource.com/c/go/+/541015
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Jes Cok <xigua67damn@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>