[llvm] llvm-shlib: Fix mingw dll exports (PR #148772)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> > Oh, also: Before merging, I'd suggest removing the CC mention in the PR description, according to https://discourse.llvm.org/t/forbidding-username-in-commits/86997.
> 
> It's not in the commit message, I just added it in the description after.

Oh, I see. When merging via the github UI, the default commit message ends up taken as the PR description though, so unless extra care is taken, it would end up included if it is part of the description.




> > This was implemented on the linker side in both LLD and binutils ld.bfd, and on the compiler side in Clang - but I didn't try to implement it in GCC.
> 
> Yes, I was aware of that, although I'm still missing why that implies that `LLVM_ALWAYS_EXPORT` can't be `__declspec(export)` in this case (while still using hidden visibility to add the extra drectve). Can you fill in the missing link for me?

I'm not entirely sure - I haven't followed the nitty gritty details about that effort yet. I suppose the thing is that as we do have some of those attributes expanding to hidden visibility, the opposite then also ends up being default visibility. Opposing hidden visibility with dllexport would be a weird combination.

https://github.com/llvm/llvm-project/pull/148772