Jonsykkel’s Pest “station” was written in C.

You’ll see it referenced in the logs:

• The log link http://zzz.st/code/smalpest/tree/src/utf8.c points to a C source file for his station implementation.
• He talks about building and running the station with C‑based code (e.g., “smalpest” is a C project).

So, if you’re looking to dig into or compile Jonsykkel’s Pest station, start with the C codebase.