[clang] [clang] Fix loss of `dllexport` for exported template specialization (PR #93302)

[via cfe-commits]

https://github.com/zmodem requested changes to this pull request.

> The import of a definition/specialization is already a bit of an anomaly, so dropping dllimport is probably reasonable.

Well, you're exporting a specialization. How is it going to get imported?

Perhaps me leaving the definition in there was unnecessary. How about just:

```
template<>
bool __declspec(dllimport) s::f<true>();
```
(https://godbolt.org/z/nqE7zPWYP)

Anyway, my point is that your patch is only working around half the bug. It seems to me that the proper fix has to be to get the attributes right in the AST.

https://github.com/llvm/llvm-project/pull/93302