[clang] [clang] Generate nuw GEPs for struct member accesses (PR #99538)

[Hari Limaye via cfe-commits]

hazzlim wrote:

> > `CGBuilder` is just aiming to provide an `Address` overload of LLVM's `CreateStructGEP`. It seems wrong for two overloads to have subtly different behavior.
> > Is there a reason why LLVM's `CreateStructGEP` doesn't add `nuw` itself?
> 
> Good point - I can see that it makes more sense to add the flag there.
> 
> I can rework this patch to do this. Before doing so - do people think it still makes sense to do add the flag in ‘llvm::CreateStructGEP’, given that as @nikic points out we can infer the flag at the IR level?

@rjmccall I've reworked this patch so that the nuw flag is added in LLVM's `CreateStructGEP` directly.

https://github.com/llvm/llvm-project/pull/99538