[clang] [Clang] Loop over FieldDecls instead of all Decls (PR #99574)

[Bill Wendling via cfe-commits]

bwendling wrote:

So is it enough to test if the FieldDecl exists in the CGRecordLayout before asking for the FieldNo? When I do that, there are some other subtle changes that occur, though maybe those are from other changes...

https://github.com/llvm/llvm-project/pull/99574