Amy W

Breaks build on 11... working on this. removing -Werror would also work, but avoiding warnings is... better.

Compiles on macOS 12 and macOS 11.5, I don't have anything else to test. As documented in comments this uses clang features to gate the new functionality and C pragmas...

I sent a pull request with a fix, it's available from my fork as branch fix-io-main.

Builds on macOS 13 as well.