I think it's looking for -lsll and not -1ssl ;-)
It cannot find the SSL libraries on your system. Did you pass the location during the ./configure ?
something like that --with-ssl-dir=/to/your/ssl/dir
Also you have to write "/usr/local/ssl/lib" in "/etc/ld.so.conf", it will be better.
Did you remove the original ssl package from slackware-8.1 ?
Anyway, you can DL and use the slackware packages from KDE's ftp. I build them and they are working great