tn5250: don't reference SSLv2/v3 functions if openssl is built without them

Fixes:
http://autobuild.buildroot.net/results/83e/83e29482cad6adef18a0e97bc8e75df302467dbb/



The recent openssl security bump disabled SSLv2 support, but tn5250 was
still referencing SSLv2 functions breaking the build.

Include a patch from OpenBSD to only reference the SSLv2 / SSLv3 symbols if
openssl is built with support for them.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>