emerge --search mod_ssl

Не оно?

eix -sS mod_ssl
* www-apache/mod_gnutls
     Available versions:  0.5.5 {ssl}
     Homepage:            http://www.outoforder.cc/projects/apache/mod_gnutls/
     Description:         mod_gnutls uses GnuTLS to provide SSL/TLS encryption for Apache2, similarly to mod_ssl

или так

emerge --searchdesc mod_ssl
Searching...    
[ Results for search key : mod_ssl ]
[ Applications found : 1 ]

*  www-apache/mod_gnutls
      Latest version available: 0.5.5
      Latest version installed: [ Not Installed ]
      Size of files: 232 kB
      Homepage:      http://www.outoforder.cc/projects/apache/mod_gnutls/
      Description:   mod_gnutls uses GnuTLS to provide SSL/TLS encryption for Apache2, similarly to mod_ssl

USE=ssl emerge apache . поставить mod_ssl

На другой системе есть. В 

slep@mini /var/tmp/portage/sys-auth/sssd-1.4.0/work/sssd-1.4.0 $ qlist apache |grep mod_ssl
/usr/lib64/apache2/modules/mod_ssl.so
/usr/include/apache2/mod_ssl.h
/etc/apache2/modules.d/40_mod_ssl.conf

P.S mod_gnutls,равно как и mod_nss не то, хотя и выполняют аналогичную функцию