Cygwin: get_user_groups: fetch a user's group list from identification token

Cygwin: get_user_groups: fetch a user's group list from identification token

NetUserGetGroups and NetUserGetLocalGroups sometimes take a lot of time
(up to more than 2 mins) for no apparent reason.

Call s4uauth to generate an identification token for the user and fetch
the group list from there.  This is *much* faster.

Keep the old code only for the sake of WOW64 on Vista and Windows 7,
which don't implement MsV1_0S4ULogon.

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