Building snowflake for macOS takes a long time

For #40046 I was rebuilding both obfs4 and snowflake for all platforms/architectures we support and realized that in particular the snowflake build for macOS takes an insane amount of time. It's been several hours, I think, while I don't see anything that is remotely similar in builds for other platforms.

Executing the build script itself is no problem. Rather, rbm spends a huge time between the respective build script runs (I've not checked what it does nor how long exactly it takes yet).

Maybe I am hitting #33289 (closed) here or a variant of it, not sure.