[clang] [llvm] [clang][X86] Return Win64 __int128 indirectly (PR #210358)

[via cfe-commits]

oltolm wrote:

I added a note about ABI change to the release notes. I also fixed a problem with lowering libcalls. A 128-bit struct is already returned indirectly on Windows, so now `i128` and `stuct { i64; i64}` will be handled in the same way.

https://github.com/llvm/llvm-project/pull/210358