Elegant. Last week I was wondering about this since we have some cases where the subdir is a target ISA like x86_64, aarch64, etc. (i.e. `src/math/`, and other cases we have an OS like linux, darwin, windows (i.e. `src/__support/OSUtil`). I guess src/__support/OSUtil and src/sys are cases where we'd need to recurse deeper. But for now, I'm happy with this addition. It makes sense to retain the TODO at the top of this function since we'll probably be revisiting this imminently.

So I was thinking about these POSIX defined functions (none of this needs to be solved in this PR, but is perhaps worth thinking about how we can do something better for POSIX functions in the future). It is possible to create a hyperlink to a page about them, example: https://pubs.opengroup.org/onlinepubs/009604499/functions/kill.html Perhaps we either add more specialized handling of the 'defined' field to support URLs, or use a different field. IDK yet.