[llvm] [IR] Add TargetExtType::CanBeAlloca property (PR #99016)

[Nicolai Hähnle via llvm-commits]

nhaehnle wrote:

What's the status of this? It seems reasonable to me. In terms of the name, I would slightly prefer something that relaxes restrictions instead of adding them, so perhaps `CanBeStack` (to cover both byval and alloca)?

https://github.com/llvm/llvm-project/pull/99016