[clang] [clangd] Fix C++20 modules crash (PR #81919)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 requested changes to this pull request.

This is not wanted. While we have a policy to revert patches if the patches break existing codes, the C++20 modules support in clangd is literally broken: https://github.com/clangd/clangd/issues/1293

Also the ability to skip ODR checks is an important feature to modules. So I don't think we should revert this now.

Also I don't understand why it can make clangd to crash. A test will be helpful for us to understand what happened.

https://github.com/llvm/llvm-project/pull/81919