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

[via cfe-commits]

zmodem wrote:

> The odd thing is that this behaviour doesn't change on the main branch or at least not with the version of it that I tried on Friday.

I could have sworn it failed... but I was also using main from a few weeks ago. I think the test doesn't fail anymore because sized delete was enabled in 130e93cc26ca9d3ac50ec5a92e3109577ca2e702. Maybe we should specify -fno-sized-deallocation or update the test somehow.

> shouldn't there be a test case added for the dropping of dllexport?

I can't think of a test case that would hit it.

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