[clang] [clang] Pass fp128 indirectly and return in xmm0 on Windows (PR #115052)

[Trevor Gross via cfe-commits]

tgross35 wrote:

I updated this PR to pass indirectly and make the xmm0 return explicit, identical to `i128`. This does not match GCC exactly since GCC's `__float128` returns on the stack, unfortunately meaning cross-implementation is still broken. I don't think that needs block the changes to Clang's here however, I plan to send patches to GCC returning in xmm0, which will match the behavior in this PR.

This should be ready for a review. Libcall changes are in https://github.com/llvm/llvm-project/pull/128848, that should land at the same time.

https://github.com/llvm/llvm-project/pull/115052