[clang] [C++20][Modules] Fix crash when function and lambda inside loaded from different modules (PR #109167)

[Ilya Biryukov via cfe-commits]

ilya-biryukov wrote:

> > Here is the reproducer that crashes at head. [lambdas.tgz](https://github.com/user-attachments/files/17329901/lambdas.tgz)
> 
> I reproduced this issue on my machine and confirm that it is indeed due to my changes. #111992 has fix that seems to fix the reproducer and doesn't introduce new issue as far as I know. @ilya-biryukov could you please try it on your full test case?

I've checked #111992 and it does fix the problem, so let's land it?

https://github.com/llvm/llvm-project/pull/109167