[clang] [CodeGen][ObjC] Invalidate cached ObjC class layout information after parsing ObjC class implementations if new ivars are added to the interface (PR #126591)

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AZero13 wrote:

I'd like to take this a step further.

What if we can also incorporate this with the knowledge that base classes with their implementation can also be subject to this:

https://github.com/llvm/llvm-project/pull/85465

What do you think? @ahatanak 

https://github.com/llvm/llvm-project/pull/126591