[clang] [Clang] Handle structs with inner structs and no fields (PR #89126)

[Eli Friedman via cfe-commits]

https://github.com/efriedma-quic approved this pull request.

LGTM

Please don't forget to fix CountCountedByAttrs... but it's fine if it's in a followup.

https://github.com/llvm/llvm-project/pull/89126