[Bug c++/86974] Support Clang's require_constant_initialization attribute

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86974

--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
One can't take __has_cpp_attribute support for granted, so perhaps that needs
to be wrapped inside ifdef.