[clang] Fix to attribute plugins reaching an unreachable (PR #70877)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> Can you please add a more detailed description of the problem and what the fix actually is. The description is what ends up in the git log and it is important that we have enough details there to understand the PR and what changes it makes.
> 
> I do not see a test, can this fix be tested?

We could add a test with a `// REQUIRES: plugins, examples` line on the RUN line. We don't have very many tests for plugins in Clang currently, but adding one here would help catch regressions.


https://github.com/llvm/llvm-project/pull/70877