[Bug c++/120635] Support something like [[clang::no_specializations]] attribute

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120635

--- Comment #2 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
And basic_format_context for https://wg21.link/lwg3975.