[clang] [clang][ASTImporter] Fix AST import if anonymous namespaces are merged (PR #128735)

[Shafik Yaghmour via cfe-commits]

https://github.com/shafik commented:

I did not fully understand this part of the summary `I did not check for other possibilities for namespaces that are not in a TU or namespace but at least the code should handle all cases` but I take it there are cases you are not testing? 

Is there a reason not to add those tests and at least if they don't pass, they can fixed a follow-up PR but we then at least have failing tests we know we need to address?

https://github.com/llvm/llvm-project/pull/128735