Switch rustc::internal from deny to warn

These should still obey deny-warnings.

Author: jyn514

src/bootstrap/check.rs

@@ -321,7 +321,7 @@ macro_rules! tool_check_step {
                 }
 
                 // Enable internal lints for clippy and rustdoc
-                // NOTE: this doesn't enable lints for any other tools unless they explicitly add `#![deny(rustc::internal)]`
+                // NOTE: this doesn't enable lints for any other tools unless they explicitly add `#![warn(rustc::internal)]`
                 // See https://github.com/rust-lang/rust/pull/80573#issuecomment-754010776
                 cargo.rustflag("-Zunstable-options");
 

src/librustdoc/lib.rs

@@ -16,7 +16,7 @@
 #![feature(type_ascription)]
 #![feature(iter_intersperse)]
 #![recursion_limit = "256"]
-#![deny(rustc::internal)]
+#![warn(rustc::internal)]
 
 #[macro_use]
 extern crate lazy_static;

src/tools/clippy/clippy_lints/src/lib.rs

@@ -17,7 +17,7 @@
 // warn on lints, that are included in `rust-lang/rust`s bootstrap
 #![warn(rust_2018_idioms, unused_lifetimes)]
 // warn on rustc internal lints
-#![deny(rustc::internal)]
+#![warn(rustc::internal)]
 
 // FIXME: switch to something more ergonomic here, once available.
 // (Currently there is no way to opt into sysroot crates without `extern crate`.)

src/tools/clippy/src/driver.rs

@@ -4,7 +4,7 @@
 // warn on lints, that are included in `rust-lang/rust`s bootstrap
 #![warn(rust_2018_idioms, unused_lifetimes)]
 // warn on rustc internal lints
-#![deny(rustc::internal)]
+#![warn(rustc::internal)]
 
 // FIXME: switch to something more ergonomic here, once available.
 // (Currently there is no way to opt into sysroot crates without `extern crate`.)