[libcxx-commits] [libcxx] [libc++][Android] Always redirect <stdatomic.h> to <atomic> (PR #143036)

[Nikolas Klauser via libcxx-commits]

philnik777 wrote:

> > @AaronBallman It seems like you're concerned about removing the `_Atomic(T)` extension, and I understand that. What would you think of merely adding a warning that says "you should include <stdatomic.h> to get consistent behavior"? The rest of the plan can stay the same: libc++ always provides `<stdatomic.h>` in all standard modes and uses `_AtomicExt` under the hood.
> 
> So we'd end up with `_Atomic` and `_AtomicExt` and they're different (incompatible) types with different semantics? Won't this still cause ABI compatibility issues for libc++ because under the hood std::atomic will be `_Atomic` in older libc++ and `_AtomicExt` in newer libc++?
> 
> Do you envision us adding additional builtins for the new `_AtomicExt` type as well?

Personally I envisioned it simply as adding `ALIAS("_AtomicExt", _Atomic, KEYALL)` to `TokenKinds.def`, except that its usage isn't diagnosed in C++.

https://github.com/llvm/llvm-project/pull/143036