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

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

@petr-polezhaev please update the mail address. We don't like github.reply mail address.

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