llvm: unions which are equivalent to enums are not by-ref
The LLVM backend lowers unions where all fields are zero-bit as
equivalent to their backing enum, and expects them to have the same
by-ref-ness in at least one place in the backend, probably more.
Resolves: #23577
ba6abd71c2mlugg committed on 8/13/2025, 10:36:16 AMparent38ba425