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

[Dmitry Polukhin via cfe-commits]

dmpolukhin wrote:

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

Yes, I would like to create a test case to don't regress this feature in future. I need to reduce libc++ `functional` header to something smaller.

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