Auto merge of #108955 - Nilstrieb:dont-use-me-pls, r=oli-obk

Add `internal_features` lint

Implements https://github.com/rust-lang/compiler-team/issues/596

Also requires some more test blessing for codegen tests etc

`@jyn514` had the idea of just `allow`ing the lint by default in the test suite. I'm not sure whether this is a good idea, but it's definitely one worth considering. Additional input encouraged.

compiler/rustc_middle/src/lib.rs

@@ -64,6 +64,7 @@
 #![feature(macro_metavar_expr)]
 #![recursion_limit = "512"]
 #![allow(rustc::potential_query_instability)]
+#![cfg_attr(not(bootstrap), allow(internal_features))]
 
 #[macro_use]
 extern crate bitflags;