[clang] [Clang][Sema]: Allow flexible arrays in unions and alone in structs (PR #84428)

[Erich Keane via cfe-commits]

https://github.com/erichkeane requested changes to this pull request.

Left my comment on the main list, but I don't see this as a well motivated change, and even if GCC supported it, it would still be a very difficult to motivate extension without massive historical workloads already using it.

In general, I don't think this is something we'd want to do either.

https://github.com/llvm/llvm-project/pull/84428