I found libevent on homebrew, but where is ppp-dev? Neither homebrew nor MacPorts seems to have it.
+1 where is ppp-dev? I saw that there is a macport for this item, but how is it built with this dependency?
I don't know if you have already figured it out or not, but it should be as simple as to install Mac OS-X development headers and toolchains (pre-req for ports project). Then simply upgrade your portage directory, and type "sudo port install sstp-client". For exact syntax, please consult the macport tutorial / man pages.