bug#25061: consider adding %COMPAT to default gnutls priority string

[Eli Zaretskii]

> From: Ted Zlatanov <tzz@lifelogs.com>
> Date: Sat, 16 Dec 2017 18:34:51 -0500
> Cc: wingo@igalia.com, 25061@debbugs.gnu.org, ludo@gnu.org,
>       michael.albinus@gmx.de, larsi@gnus.org
> 
> Considering 14.04 is pretty old, and AFAIK we can't check if %DUMBFW is
> supported, we don't have good options:
> 
> 1) undo the change (please don't just revert the commit)
> 2) document the breakage
> 3) start setting the default conditionally based on GnuTLS version (ugh)
> 
> Any other options?

If no other ideas come up, I don't see 3) as such a terrible choice.

Thanks.