[Bug c++/109169] Feature request: Allow omitted template prompts

["steve_green at qq dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109169

--- Comment #6 from steve02081504 <steve_green at qq dot com> ---
Created attachment 54696
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54696&action=edit
temp.cpp

(In reply to Andrew Pinski from comment #4)
> You provide a full example of what you want?
> Because right now your example your provided does not even compile with msvc.

Strangely enough, when I tried to reproduce this requirement, I found that the
sample code I had written would compile.
```c++
#include <concepts>
template<class T>
struct A {
        template<class U>
        static constexpr bool a = ::std::is_base_of_v<T, U>;
};
template<class T>
A<T> a{};
int      main() {
        return a<int>.a<int>;
}
```
I had no choice but to attach the files I couldn't get to compile and pass in
the attachment.
I didn't understand whether gcc could compile such things or not......