[Bug c++/104111] New: Concept evaluation depends on context where it was first checked

["fchelnokov at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104111

            Bug ID: 104111
           Summary: Concept evaluation depends on context where it was
                    first checked
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: fchelnokov at gmail dot com
  Target Milestone: ---

Please consider a concept and a class definitions:
```
template<class T>
concept has_private = requires(){ &T::private_;};

class B{
   int private_;
   friend class A;
};
```

If we first check the concept inside `A` then it will be always evaluated to
true:
```
class A{
   static_assert( has_private<B> );
};
static_assert( has_private<B> );
```
Demo: https://godbolt.org/z/eYP6Tq7Y7

But if we first check the concept outside `A` then it will be always evaluated
to false:
```
static_assert( !has_private<B> );
class A{
   static_assert( !has_private<B> );
};

```
Demo: https://godbolt.org/z/vsTx4oTaE

Clang has the same behavior. At the same time MSVC always evaluates the concept
to false, and it looks correct, because context evaluation shall not depend on
the context.

Related discussion: https://godbolt.org/z/vsTx4oTaE