[Bug c++/125569] GCC treats a class with a deleted destructor as std::is_literal_type

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125569

Ke Gong <gongke at ios dot ac.cn> changed:

           What    |Removed                     |Added
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                 CC|                            |gongke at ios dot ac.cn

--- Comment #5 from Ke Gong <gongke at ios dot ac.cn> ---
I agree with @qurong.

Although the trait `std::is_literal_type` is gone in C++20, the concept of
"literal type" is still used, for example, for determining whether a type can
be used in a non-type template parameter.

Also note that the definition of "literal type" is different in C++20. As
[basic.types]/10 in N4659 (C++17) and N4861 (C++20), the destructor is required
to be *trivial* in C++17, but *constexpr* in C++20.

Look at this:

```cpp
struct NotLiteralCpp20 {
  ~NotLiteralCpp20() = delete;
};
template <NotLiteralCpp20 x>
struct Foo {};
```

This template parameter declaration should be ill-formed because
`NotLiteralCpp20` is not a literal type, but GCC accepts it.