[Bug c++/110793] regression in optimizing unused string

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110793

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Barry Revzin from comment #0)
> Notably, 13.1 C++20 and C++23 also compiles to just xor. 
> 

Probably because we don't use the extern template declarations for C++20.