One thing to add here, I've enjoyed reasonably extensive support for `atomic_compare_exchange_strong()` and the `_explicit` variant for quite a long time (despite the need for the cache line lock on x86).

But, last I checked (the last release, early last year) MUSL still does not provide a 128 bit version, which is disappointing, and hopefully the AVX related semantics changes will encourage them to add it? :)