[libcxx-commits] [libcxxabi] [libcxx] [libc++] Split the monolithic __threading_support header (PR #79654)

[Nico Weber via libcxx-commits]

nico wrote:

This requires updating libcxx and libcxxabi at the same time.

Any opposition to replacing the includes in libcxxabi with

```
#if __has_include(<__thread/support.h>)
#include <__thread/support.h>
#else
#include <__threading_support>
#endif
```

for a while, so that projects can keep rolling libcxxabi and libcxx independently? (We have an autoroller for libcxxabi that has been working without issues for years up to this change, and we have one for libcxx that's broken pretty frequently due to libcxx changes, including right now. It'd be nice if libcxxabi could keep rolling.)

https://github.com/llvm/llvm-project/pull/79654