[llvm] [VFABI] Add support for vector functions that return struct types (PR #119000)

[Florian Hahn via llvm-commits]

https://github.com/fhahn approved this pull request.

LGTM, thanks. It's probably better to keep it as separate header, to avoid including it in many places that don't need it

https://github.com/llvm/llvm-project/pull/119000