[llvm] Implement the trampoline intrinsics for AIX. (PR #149388)

[Amy Kwan via llvm-commits]

https://github.com/amy-kwan approved this pull request.

Nit: should the title of the PR also be expanded to say that we're supporting nested arguments on AIX?

Nonetheless, I think LGTM.

https://github.com/llvm/llvm-project/pull/149388