[clang] [Sema] Call ActOnFields before late parsing in ParseStructUnionBody (PR #187166)

[Yeoul Na via cfe-commits]

rapidsna wrote:

> That said, for a change which is explicitly made to support sizeof and offsetof, shouldn't there be test cases exercising those?

Yes, but I don't think there are tests that we can currently run right now, because in upstream `counted_by` and friends can only take a declaration reference (or simple ID). Maybe existing tests working without any regression should be sufficient for now?

https://github.com/llvm/llvm-project/pull/187166