Rollup merge of #138084 - nnethercote:workspace-lints, r=jieyouxu

Use workspace lints for crates in `compiler/`

This is nicer and hopefully less error prone than specifying lints via bootstrap.

r? ``@jieyouxu``

compiler/rustc_serialize/Cargo.toml

@@ -16,3 +16,6 @@ thin-vec = "0.2.12"
 rustc_macros = { path = "../rustc_macros" }
 tempfile = "3.2"
 # tidy-alphabetical-end
+
+[lints]
+workspace = true

compiler/rustc_serialize/src/lib.rs

@@ -14,7 +14,6 @@
 #![feature(min_specialization)]
 #![feature(never_type)]
 #![feature(rustdoc_internals)]
-#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 pub use self::serialize::{Decodable, Decoder, Encodable, Encoder};