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

[Paul T Robinson via cfe-commits]

https://github.com/pogo59 commented:

Does the test exercise both modified paths? I'm guessing it only exercises GetOrCreateLLVMFunction, but I'm not a codegen expert.

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