windows: export O_FILE_FLAG_* to be used in os.OpenFile on windows

These file flags are supported by os.OpenFile since CL 699415.

Closes golang/go#73676

Change-Id: Iaf846c9cb98c1458bbc30d05ad8a331ef1f332df
Reviewed-on: https://go-review.googlesource.com/c/sys/+/700975
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>

windows/types_windows.go

diff --git a/windows/types_windows.go b/windows/types_windows.go
index 993a229..358be3c 100644
--- a/windows/types_windows.go
+++ b/windows/types_windows.go
@@ -65,6 +65,22 @@
 	15: "terminated",
 }
 
+// File flags for [os.OpenFile]. The O_ prefix is used to indicate
+// that these flags are specific to the OpenFile function.
+const (
+	O_FILE_FLAG_OPEN_NO_RECALL     = FILE_FLAG_OPEN_NO_RECALL
+	O_FILE_FLAG_OPEN_REPARSE_POINT = FILE_FLAG_OPEN_REPARSE_POINT
+	O_FILE_FLAG_SESSION_AWARE      = FILE_FLAG_SESSION_AWARE
+	O_FILE_FLAG_POSIX_SEMANTICS    = FILE_FLAG_POSIX_SEMANTICS
+	O_FILE_FLAG_BACKUP_SEMANTICS   = FILE_FLAG_BACKUP_SEMANTICS
+	O_FILE_FLAG_DELETE_ON_CLOSE    = FILE_FLAG_DELETE_ON_CLOSE
+	O_FILE_FLAG_SEQUENTIAL_SCAN    = FILE_FLAG_SEQUENTIAL_SCAN
+	O_FILE_FLAG_RANDOM_ACCESS      = FILE_FLAG_RANDOM_ACCESS
+	O_FILE_FLAG_NO_BUFFERING       = FILE_FLAG_NO_BUFFERING
+	O_FILE_FLAG_OVERLAPPED         = FILE_FLAG_OVERLAPPED
+	O_FILE_FLAG_WRITE_THROUGH      = FILE_FLAG_WRITE_THROUGH
+)
+
 const (
 	FILE_READ_DATA        = 0x00000001
 	FILE_READ_ATTRIBUTES  = 0x00000080