bug#27708: [PROPOSED] Simplify configuration of HAVE_GNUTLS3 etc.

[Ted Zlatanov]

On Sat, 15 Jul 2017 19:33:40 +0300 Eli Zaretskii <eliz@gnu.org> wrote: 

EZ> If we want to support the new APIs only starting with GnuTLS 3.4.0,
EZ> then this is a step in the right direction.  But is that the intent?
EZ> Most of the functions we need are available in much older versions,
EZ> and others since 3.2.0.  Only a few appeared in 3.4.0.  So it might
EZ> also make sense to make our code more fine-grained, not less, if we
EZ> want to make as many of these APIs available on as many platforms as
EZ> possible.

EZ> But I'm not sure what was Ted's intent, and what we want as a project.

Exactly, and I replied on emacs-devel in the same vein. I'd like to
ensure people on 3.2.x have as much functionality as possible because
they may not be able to upgrade quickly. I also worry about forward
compatibility with a future 4.x or later GnuTLS API. So I'd like
comments and votes on this.

A good starting point is
https://www.gnutls.org/manual/html_node/Cryptographic-API.html which
will show the ebb and flow of the API since the 2.x versions.

Ted