[clang] [ObjC] Check entire chain of superclasses to see if class has fixed offsets (PR #81335)

[via cfe-commits]

AtariDreams wrote:

> test seems completely inadequate — you need to test that we're doing the static layout properly, and you need to test with ivars coming from a variety of different places, including:
> 
> * ivars declared in the `@interface`
> * ivars declared in the `@implementation`
> * ivars synthesized explicitly in the `@implementation`
> * vars synthesized implicitly in the `@implementation`

I think it is the only way, otherwise it would have to be done at link time. Can we do it at link time? probably another PR would have to deal with that.

https://github.com/llvm/llvm-project/pull/81335