[dovecot/core] 0793a1: configure: Fix build with old OpenSSL without SSL_...

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 0793a1dbdfc369b60ad8aa16f4ee58cc1c238f5c
      https://github.com/dovecot/core/commit/0793a1dbdfc369b60ad8aa16f4ee58cc1c238f5c
  Author: Paul Howarth <paul at city-fan.org>
  Date:   2016-11-18 (Fri, 18 Nov 2016)

  Changed paths:
    M m4/ssl.m4
    M src/lib-ssl-iostream/iostream-openssl.c

  Log Message:
  -----------
  configure: Fix build with old OpenSSL without SSL_clear_options

SSL_clear_options was introduced in OpenSSL 0.9.8m but may be
backported to older versions in "enterprise" OS releases, so a version
check is insufficient here.

It was originally implemented as a macro but is a function in more
recent OpenSSL versions, so a test that works for both cases is needed.