FYI: the test failure is a libc++ test for directory_entry's comparison operators that expects actual member functions (e.g., operator<=) to be present. I've pushed a fix upstream, and opened #1594 to update our LLVM submodule reference to get the fixed test. Once #1594 merges, we'll need to merge it to feature/spaceship which we can then merge into this PR.

Moving this to final review despite the test failure which is addressed by #1594. If there is a problem with #1594 and we absolutely must merge this first, we can skip the failing libc++ test in this PR and re-enable in #1594.

Thanks for spaceship-izing locales and I/O so we can properly communicate with aliens! 👽 💬 📡