Auto merge of #10142 - jyn514:bin-private-link, r=ehuss

Auto merge of #10142 - jyn514:bin-private-link, r=ehuss

When documenting private items in a binary, ignore warnings about links to private items

Previously, rustdoc would warn about linking to private items in a binary, even
though cargo unconditionally documents private items in a binary.
This changes cargo to silence the warning, since it's only relevant in
cases where the private items might not be documented.

Fixes https://github.com/rust-lang/rust/issues/89600.