9d49eb76c4
Add unstable `-Zdefault-hidden-visibility` cmdline flag for `rustc`. The new flag has been described in the Major Change Proposal at https://github.com/rust-lang/compiler-team/issues/656
rustc_target contains some very low-level details that are
specific to different compilation targets and so forth.
For more information about how rustc works, see the rustc dev guide.