fc/src/filesystem.cpp:207 fails to build because it calls level(), but according to [the release notes]

(https://www.boost.org/doc/libs/1_79_0/libs/filesystem/doc/release_history.html), this was deprecated way back in 1.72.0 and by now it's long gone. Call depth() instead.

If submitting a patch to upstream, it would be best to include #ifdef guards to maintain compatibility with versions prior to 1.72, which didn't yet have depth().****