[clang] Fix build dllexport/dllimport issues when doing a shared build for Windows using GCC (PR #66881)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> This is superseded by https://github.com/llvm/llvm-project/pull/71393 which was merged now.

I'll close this one for now, as I believe the issue has been fixed differently.

https://github.com/llvm/llvm-project/pull/66881