[clang] Fix buildbot failure. (PR #86741)

[Kazu Hirata via cfe-commits]

kazutakahirata wrote:

> Now I wonder if the fix should be with the (void) or without. Have you tried it locally to see if you get the same build error?

Yes, I just tried your patch and confirmed that the unit test passes without a problem.

No, you shouldn't keep `(void)` there.  It's there just to silence the warning because the lambda is sitting unused outside the call to `PrintedDeclCXX98Matches`.  Once you bring the lambda inside the call to `PrintedDeclCXX98Matches`, the lambda is used, so you shouldn't get a warning.

https://github.com/llvm/llvm-project/pull/86741