bug#32446: Configure-time requirement for gnutls is too old

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Cc: Gavin Smith <gavinsmith0123@gmail.com>,  Ted Zlatanov <tzz@lifelogs.com>, 
>  32446@debbugs.gnu.org
> Date: Sat, 15 Sep 2018 10:44:04 -0400
> 
> I think we can keep most of the functionality: the missing APIs only
> make a difference for AEAD ciphers, which are already disabled for
> versions before 3.5.

Thanks.

Gavin, can you test this with your version of GnuTLS?