recently nmap has stopped being libressl friendly, I had to modify a few #if/#ifdefs for that.
I don't have a system with openssl, so please check that this still works on your side.
Let me know if you want me to change anything, or if you don't plan to support libressl.
Modify #if/ifdef's to be compatible with libressl
Add compatibility with LibreSSL. Closes #543