In libgadu-1.10.0 there was introduced an optional dependency on gnutls for encrypted connection support as an alternative to openssl (BTW, gnutls takes precedence by default). But there is no corresponding USE flag in the ebuild so it always links to gnutls if installed on system, even with USE=ssl. BTW I found gnutls code working more reliably than the openssl one for me (rare connection problems with openssl).
Indeed, also configure parameter corresponding to OpenSSL support was renamed (from --with-ssl to --with-openssl) so it's even more automagic now since ebuild doesn't expect this. Anyway, fixed. Thanks for reporting!