BUILD: ssl: fix again a libressl build failure after the openssl FD leak fix

BUILD: ssl: fix again a libressl build failure after the openssl FD leak fix

As with every single OpenSSL fix, LibreSSL build broke again, this time
after commit 56996dabe ("BUG/MINOR: mworker/ssl: close OpenSSL FDs on
reload"). A definitive solution will have to be found quickly. For now,
let's exclude libressl from the version test.

This patch must be backported to 1.9 since the fix above was already
backported there.