[clang] [llvm] Add missing CLANG_ABI annotations to enable building clang and llvm shared libraries on Windows (PR #188587)

[Aaron Ballman via llvm-commits]

AaronBallman wrote:

> @AaronBallman @nikic My plan to try and complete the llvm side is as follow
> 
>     1. Add all missing LLVM_ABI annotations to enable the building llvms tests, benchmarks, tools, etc, and put in a single PR which contains all of them. I'm currently trying to debug this in an external repo. I'm new to adding the annotations so its possible some of the annotations may be unneeded when I put the PR in. My intial goal will be to get something working, which can be refined through review.
> 
>     2. Add a ci which builds LLVM as a shared library on Windows to stop anyone adding an annotation(s) which breaks the build, and checks the tests pass for this build (this is effectively done as I am debugging point 1 with a Github ci, and it would just need some refinement to be included in the llvm repo itself)
> 
> 
> This could be followed by someone enabling the ids workflow to give suggestions to people on how they should annotate, in case they have annotated incorrectly.
> 
> Hopefully with the above build ci in and ids workflow on top of that, after a few months of stability I could move onto doing the clang annotations. Let me know what you think

I think that sounds like a reasonable path forward, thank you!

https://github.com/llvm/llvm-project/pull/188587