[clang] [Clang][Parser] Reject unbalanced unknown attribute arguments (PR #220259)

[Nikita Popov via cfe-commits]

nikic wrote:

Compile-time: https://llvm-compile-time-tracker.com/compare.php?from=4e7b87f0dd39f21f592ca341b33b0447ea74951b&to=f7c9a337afcd4dbbc679c2b4a9ab9c8e0e89ea66&stat=instructions:u

No impact on that test set at least.

https://github.com/llvm/llvm-project/pull/220259