[clang] [clang][CodeGen] `sret` args should always point to the `alloca` AS, so use that (PR #114062)

[Alex Voicu via cfe-commits]

AlexVlx wrote:

Gentle ping - I'd like to progress this in one form or another (target hook or extending indirect to carry an AS). If there are other ideas / strong preferences / over-my-dead-body objections, they'd be more than welcome.

https://github.com/llvm/llvm-project/pull/114062