Someone pointed it out to me a while ago. I don't think the approach is comparable to Zig, but is in a somewhat similar spirit. Like with macros, Terra contains two languages (one of them being the meta language), while Zig has general partial evaluation in just one language (also https://news.ycombinator.com/item?id=24293611). For example, in Terra, conditional compilation is a branch in the metalanguage; in Zig, it's just a branch in Zig that is partially evaluated.

BTW, even Zig's build language is just Zig!