Deny internal lints on non conflicting crates

- libarena
- librustc_allocator
- librustc_borrowck
- librustc_codegen_ssa
- librustc_codegen_utils
- librustc_driver
- librustc_errors
- librustc_incremental
- librustc_metadata
- librustc_passes
- librustc_privacy
- librustc_resolve
- librustc_save_analysis
- librustc_target
- librustc_traits
- libsyntax
- libsyntax_ext
- libsyntax_pos

src/librustc_codegen_utils/lib.rs

@@ -16,6 +16,7 @@
 #![recursion_limit="256"]
 
 #![deny(rust_2018_idioms)]
+#![cfg_attr(not(stage0), deny(internal))]
 
 #[macro_use]
 extern crate rustc;