[Bug c++/104994] extern thread_local declaration rejected in constexpr

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104994

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Ville says that P2242 did not intend to add new restrictions, so this was valid
in C++20, and should still be valid in C++23 even if control flow passes over
that non-local declaration. We might have a defect in the current draft,
because it seems to forbid it.