[clang-tools-extra] [clangd] Introduce --skip-preamble-build command line option (PR #189284)

[Aleksandr Platonov via cfe-commits]

ArcsinX wrote:

> We need to record our conclusion somewhere in clangd's release notes: "We introduced a regression that clangd can't detect the changes in headers for TU containing import in some cases. The original change detection mechanism (it can't detect changes not in preamble) already has some problems. We plan to fix it in the future. We did this to modules now as the PCH and C++20 named module don't work well and may introduce bad crashes randomly.". You can change the wording if you like.

Maybe we can do this before the release? But if you're sure we won't fix this clang problem before the next release, I'd be happy to add this information into release notes now.

https://github.com/llvm/llvm-project/pull/189284