https://bugs.winehq.org/show_bug.cgi?id=38886
--- Comment #10 from Martin Storsjö martin@martin.st --- Another pretty relevant commit:
r309744: https://github.com/llvm-mirror/llvm/commit/39bec211f05ca28c8b61d70fd5d9c030f... discussions: https://reviews.llvm.org/D35919
(The original implementation of AArch64/Win64 varargs in the previous linked commits was buggy for a lot cases, while this version has been in use without any known issues now for long over a year.)