[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:

Discuss with @ChuanqiXu9  offline, I'm trying to find another, more meaningful solution; this problem might also exist when clang processes PCH.I'm trying to find another, more meaningful solution; this problem might also exist when clang processes PCH.

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