[clang] [clang-tools-extra] [clang] Don't add documentation comments to the AST if not requested (PR #206363)

[Alexis Engelke via cfe-commits]

aengelke wrote:

This causes a huge perf regression: https://llvm-compile-time-tracker.com/compare.php?from=aa1058e34a6127df91898829b0e60cbae3111cbf&to=e046dce4a4c80610b49d67bc02c85f86b1a6353d&stat=instructions:u

Can we revert this?

https://github.com/llvm/llvm-project/pull/206363