[clang] [clang] fix crash in friend definition (PR #186398)

[via cfe-commits]

Serosh-commits wrote:

> The problem here looks fairly simple to understand what goes wrong. Example:
> 
> ```c++
> struct X {
>   void f2();
> };
> struct Y {
>   friend void X::f2() {}
> };
> ```
> 
> Your logic for filtering the diagnostic based on the nested name specifier being of namespace / global kind only is not right, as this case otherwise does not get covered by any diagnostics later.

<img width="841" height="565" alt="image" src="https://github.com/user-attachments/assets/8dae2391-7e34-488d-9535-89f6b37e3b0c" />
oh shoot  i actually thought that and asked u that must be the problem to make sure but yeah i didn't realised i can't review 
yeah u are right let me refactor it thanks for ur review

https://github.com/llvm/llvm-project/pull/186398