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

[hjl.tools at gmail dot com]

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

--- Comment #5 from H.J. Lu <hjl.tools at gmail dot com> ---
But

CR4.FSGSBASE

FSGSBASE-Enable Bit (bit 16 of CR4) — Enables the instructions RDFSBASE,
RDGSBASE, WRFSBASE, and WRGSBASE.

>From user space, we can't tell if FSGSBASE is enabled.