[clang-tools-extra] [clangd] Add tweak to override pure virtuals (PR #139348)

[Qinkun Bao via cfe-commits]

qinkunbao wrote:

Hi, it looks like it still needs some time to fix the build bot errors. I am going to revert this PR according to https://llvm.org/docs/DeveloperPolicy.html#patch-reversion-policy Please reland this PR after the error is fixed. Thanks!

https://github.com/llvm/llvm-project/pull/139348