[clang] [clang-tools-extra] [clang] Hide the `DiagnosticOptions` pointer from `CompilerInvocation` (PR #106274)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

@kadircet Can you please check my assumption on the clangd part? The `.reset()` call was introduced in 27ade4b554774187d2c0afcf64cd16fa6d5f619d.

https://github.com/llvm/llvm-project/pull/106274