[clang] [clang][NFC] constify or staticify some CGRecordLowering fns (PR #82874)

[Eli Friedman via cfe-commits]

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

I'm not sure there's really much point to passing around a const reference to a CGRecordLowering; all the uses are in one file, so const-correctness doesn't seem to help that much.

But if you want to do it this way, that's fine; LGTM

https://github.com/llvm/llvm-project/pull/82874