ssmtp: enhanced to build without openssl

mail/ssmtp/ssmtp.conf

@@ -17,7 +17,9 @@
 #!> Try `hostname --help' for more information.
 var_append makeinstopt ' ' 'GEN_CONFIG=true'
 
-var_append extraconfopt ' ' '--enable-ssl'
+if pkginstalled openssl; then
+	var_append extraconfopt ' ' '--enable-ssl'
+fi
 var_append extraconfopt ' ' '--enable-md5auth'
 
 hook_add postmake 5 'ssmtp_install_conf'