[clang] [C++20] [Modules] [Serialization] Delay marking pending incomplete decl chains until the end of `finishPendingActions`. (PR #121245)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

Can you reduce your modules test case into a self contained project with build system?

If so, you can use [cvise](https://github.com/marxin/cvise) for reducing a whole project directory recursively in one invocation.

https://github.com/llvm/llvm-project/pull/121245