Hello,
it is currently impossible to build nagios-plugins against an OpenSSL installation without SSLv3 support because plugins/sslutils.c uses SSLv3 functions without checking whether they even exist. Such a check is present for the SSLv2 support, but as SSLv3 is also ancient and has known weaknesses, it is getting more likely to encounter OpenSSL installations that have SSLv3 support disabled.
The FreeBSD port of nagios-plugins is currently using the following patch to allow the build to succeed; I think it can be used verbatim here, too: