Add UsePrivilegeSeparation=no for cygwin.

Reported by Yang Tse <yangsita@gmail.com>

tests/ssh2.sh

@@ -18,8 +18,11 @@ export PUBKEY
 
 chmod go-r $srcdir/etc/host*
 $SSHD -f /dev/null -h $srcdir/etc/host \
-    -o 'Port 4711' -o 'Protocol 2' \
-    -o "AuthorizedKeysFile $srcdir/etc/user.pub" -D &
+    -o 'Port 4711' \
+    -o 'Protocol 2' \
+    -o 'UsePrivilegeSeparation no' \
+    -o "AuthorizedKeysFile $srcdir/etc/user.pub" \
+    -D &
 sshdpid=$!
 
 trap "kill ${sshdpid}; echo signal killing sshd; exit 1;" EXIT