[cfe] namespace confusion after wrong constructor declaration

[eernstg]

Consider the test co19/LanguageFeatures/Constructor-tear-offs/unnamed_constructor_A03_t07, line 46.

At this point, the class D declares a member named D, that is, a constructor. However, the test run reports the following error:

- Unexpected error at line 46, column 3: 'D' is already declared in this scope.

but there is no other declaration in the body of D with that name.