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

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Generally is looking good to me, though I think there are some additional tests to add. @erichkeane how are you feeling about the current shape of things?

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