Cygwin: fix up cached DOS file attributes after file creation

Cygwin: fix up cached DOS file attributes after file creation

The file attributes after creating a file are not necessarily
identical to the attributes we passed as argument to NtCreateFile.
This results in subsequent operations like fchmod or facl to
set the DOS file attributes to unexpected values.

The fix is to request file attributes from the OS after file creation
and cache those.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>