[Bug c++/102350] __builtin_source_location not available in earlier language modes

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102350

--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It wouldn't work correctly in all cases, as Jakub points out, because
std::source_location::current() is part of the magic.

And I'm not convinced we want/need to support those uses.