[Bug middle-end/96200] Implement __builtin_thread_pointer() and __builtin_set_thread_pointer() if TLS is supported

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96200

--- Comment #8 from Florian Weimer <fw at gcc dot gnu.org> ---
(In reply to H.J. Lu from comment #7)
> Give that the tcb field is setup by the C run-time on Linux/x86, should
> it be provided by a run-time header file?

Yes, it seems reasonable to me. Ideally, it would be documented in the ABI
manual as well.