[clang] [CIR] Pointer and vptr width from a CIR-native data-layout entry (PR #204185)

[Akshay K via cfe-commits]

kumarak wrote:

Thanks, @andykaylor, for the feedback. I pushed commits addressing your comments.

On mixing data layouts with different pointer sizes: the representation is built for it. I used `SpecAttr` keyed on `cir.ptr`, the same structure the MLIR ptr dialect uses for per-memory-space pointer sizes. But this isn't handled in the PR yet, and I have flagged the spot that needs fixing with TODOs. 

Would you prefer to handle it in this PR, or do you want a follow-up PR for handling per memory space? I am happy to do it either way.

> This looks like a good step forward, but I have a couple of requests.
> 
> Do you have any plans for mixing data layouts with different pointer sizes for different targets in the same module? I know we don't currently generate that condition, but we'd like to in the near future.



https://github.com/llvm/llvm-project/pull/204185