[llvm] [X86] Correctly call 16 byte atomic helpers on x86_64 Windows (PR #181356)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> Does this also fix #136428 ?

Thanks; yes, that seems to be exactly this issue.

Thanks for the reviews; unless @nikic or someone else objects, I'll merge this early next week, and then request backporting it to 22.x.

https://github.com/llvm/llvm-project/pull/181356