If you're wondering where the content actually is, take a look at the commit, where comments are written alongside the code:

https://github.com/brson/annotated-std-rs/commit/e50c2b16455...

Still not very much content - not sure if this was worth posting yet

No, but it demonstrates a neat way to use github. Next time someone asks me to annotate some code, rather than fighting with a word doc or throwing gazillions of comments inline, I'm going to try this out.

I suspect this is the kind of thing that wasn't posted to HN by the original content creator

It looks like Rust picks up where GCC left off in terms of compile options. I hope this gets cleaned up in later releases as features either become stable or are dropped. This looks like heavy technical debt from the startup phase.

Stabilizing the features used in the standard library is an ongoing process, yes.