cygwin: drop explicit O_TEXT

Cygwin binaries should not enforce text mode these days, just
use text mode if the underlying mount point requests it

Signed-off-by: Corinna Vinschen <vinschen@redhat.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8275)