tautological warnings for is_constant_evaluated not emitted in c++23/26 modes

[cor3ntin]

for

int main() {
   if constexpr(std::is_constant_evaluated()) { }
}

We usually warn

'std::is_constant_evaluated' will always evaluate to 'true' in a manifestly constant-evaluated expression [-Wconstant-evaluated]

However this warning is gone in c++23 mode

https://godbolt.org/z/KKPKvveGM

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: cor3ntin (cor3ntin)

for

int main() {
   if constexpr(std::is_constant_evaluated()) { }
}

We usually warn
> 'std::is_constant_evaluated' will always evaluate to 'true' in a manifestly constant-evaluated expression [-Wconstant-evaluated]

However this warning is gone in c++23 mode

https://godbolt.org/z/KKPKvveGM