[clang] [Clang] Implement the 'counted_by' attribute (PR #76348)

[Yeoul Na via cfe-commits]

rapidsna wrote:

> This prints a wrapped calculation instead of the expected "0".

Shouldn't `getDefaultBuiltinObjectSizeResult` return `-1`? Have you tried `-2` to see if it's returning the negative count value or it happens to be equal to the default value?

https://github.com/llvm/llvm-project/pull/76348