According to https://curl.haxx.se/docs/install.html
One has to pass --without-ssl before specifying the tls backend one wants to use. If I don't do so, the games fails to link on OSX 10.9.5 Mavericks.
See the discussion here: https://wildfiregames.com/forum/index.php?/topic/24796-a23-re-release-preparation/&page=4
One also has to change the url for libsodium because Mavericks does not support the SSL protocol used on the website, but it didn't seem logical to include it in that revision because it requires a bit more changes to make it work. (The github url has the version in the path)
by this one: