[libc-commits] [libc] [libc][threads] Add architecture-specific Thread Control Block definitions (PR #220607)

[Pavel Labath via libc-commits]

labath wrote:

The followup patch is going to look approximately like [this](https://github.com/llvm/llvm-project/pull/220921/changes/5d63618ef2f15eb6a4a676045390ffed15245ddc).

https://github.com/llvm/llvm-project/pull/220607