https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106111
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Looks like we don't warn about any keywords with any -Wc++NN-compat options:
int decltype, constexpr, consteval, requires, noexcept, alignof, alignas;
GCC doesn't warn about any of these, Clang only warns about two:
$ g++ -std=c++03 r.C -c -Wc++20-compat
$ clang++ -std=c++03 r.C -c -Wc++20-compat
r.C:1:26: warning: 'consteval' is a keyword in C++20 [-Wc++20-compat]
int decltype, constexpr, consteval, requires, noexcept, alignof, alignas;
^
r.C:1:37: warning: 'requires' is a keyword in C++20 [-Wc++20-compat]
int decltype, constexpr, consteval, requires, noexcept, alignof, alignas;
^
2 warnings generated.
