Sets the accessibility of types and fields in DWARF using
`DW_AT_accessibility` attribute.
`DW_AT_accessibility` (public/protected/private) isn't exactly right for
Rust, but neither is `DW_AT_visibility` (local/exported/qualified), and
there's no way to set `DW_AT_visbility` in LLVM's API.
Signed-off-by: David Wood <david@davidtw.co>
