Rust's `i128` return ABI does not agree with Clang and GCC on Windows targets

[tgross35]

Originally reported at rust-lang/lang-team#255 (comment), Clang and GCC-MinGW return __int128 in xmm0. Rust currently returns it on the stack.

@wesleywiser has a proposed patch to make Clang return on the stack for -msvc targets, while keeping the behavior for MinGW wesleywiser/llvm-project@b2f8b83.

Rustc could probably just change the Windows ABI to always return in xmm0 for now, and then if the Clang patch lands we can change this to apply only to MinGW.

Demo: https://godbolt.org/z/o9h8We69o