[cxx-interop] Deserialization failure with namespaces
Namespaces are imported into the __ObjC module. As a result, when a
Swift module is serialized, it refers to the declarations in the __ObjC
namespace. However, during deserialization, these declarations are found
in their original C++ module. The first failure triggered a recovery
that populated the __ObjC module so subsequent lookups succeed.
This PR makes sure we do not consider a declaration from the __ObjC
module that was found in a different clang module problematic.
Fixes #82318
