[clang-tools-extra] [clangd] Support .clangd command line modifications for C++ modules (PR #122606)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 approved this pull request.

Thanks. This looks good to me. And please give @kadircet some time to give it a look. I'll try to land this in the next week if no more comments came in.

https://github.com/llvm/llvm-project/pull/122606