[llvm] [Support] Add missing LLVM_ABI annotations in Atomic.h (PR #152768)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

FWIW, I may have spoken too soon, re

> This fixes building LLD for mingw targets with LLVM_BUILD_LLVM_DYLIB_VIS=ON.

As in, it does fix it, if building with Clang, but it still mostly uses `__attribute__((visibility("default")))` and `hidden` in that configuration (and doesn't work as is out of the box in builds with GCC) - it did seem a bit too good to be true. It will require a number of further tweaks to take these annotations fully in use in the form of dllexport/import for mingw - I'll try it out soon.

But this fix is one step on the way in any case.

https://github.com/llvm/llvm-project/pull/152768