The pkgconfig bit may not be necessary, I just wanted to mention it in review email in case it was relevant. pkg-config is one of those mechanisms that is often attempted/autodetected in build systems, so builds can be non deterministic if ports logic is not bang on.

There's plenty of systems that have pkg-config installed when building ports, unrelated to the port build in question. Clean-room environments like poudriere wont pick this up without specific testing.

One thing you can try is to unconditionally add the dependency on pkg-config and see if/how the build/package changes with/without it installed.