That produces a bit of a chicken and egg probablem for a stdlib overhaul. Compilers and libc implementations don't have a strong reason to implement safer APIs, because if it is non-standard then projects that want to be portable won't use it , but it won't get standardized unless they do add safer APIs.
So the best hope is probably for a third party library that has safet APIs to get popular enough that it becomes a de facto standard.
I think the real failing is that new language features then must be prototyped by people who have a background in compilers. That's a very small subset of the overall C community.
I don't have any clue how to patch clang's front end. I'm not a language or compiler person. I just want to make stuff better. There needs to be a playground for people like me, and hopefully lib0xc can be that playground.
By adding to the language itself, you mostly make stuff worse. The major reason why C is useful is its quite stable syntax and semantics. Language is typically not the area where you want to add code. It's much better (and much easier) to invent function APIs. See how they shake out, if they're good you might get some adoption.