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

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Empty fields sometimes don't have a corresponding LLVM field number, in order to make the layout work correctly.  We slightly extended the cases where this applies recently; see #96422.

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