[clang] [clang-tools-extra] [clangd] Handle C++20 annot_module_name token and don't discard successfully built modules when on fail (PR #187858)

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yronglin wrote:

> Weird. When I try to reproduce again, I found it stop crash now on trunk. My commit hash is [983b202](https://github.com/llvm/llvm-project/commit/983b2023ddc366369ef1d5b8a705e87466ae7991)

Thanks! Let me try 983b2023ddc366369ef1d5b8a705e87466ae7991. 

https://github.com/llvm/llvm-project/pull/187858