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

[Hans Wennborg via cfe-commits]

zmodem wrote:

I guess that means this patch doesn't have any useful behavior change until counted_by etc. supports more complex expressions. Since we know that is coming, and this needs doing sooner or later, I suppose this could be okay.

Maybe you could check in the desired tests anyway, but with TODOs to update the expectations, similar to this example: https://github.com/llvm/llvm-project/blob/9fe04e0c52ca644c8c5d07589f7f5a6752557741/clang/test/Sema/attr-counted-by-or-null-late-parsed-struct-ptrs.c#L114-L126

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