Migrate most of rustc_builtin_macros to diagnostic impls

Co-authored-by: Joe ST <joe@fbstj.net>
Co-authored-by: Michael Goulet <michael@errs.io>

compiler/rustc_builtin_macros/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(if_let_guard)]
 #![feature(is_sorted)]
 #![feature(let_chains)]
+#![feature(lint_reasons)]
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_quote)]
 #![recursion_limit = "256"]
@@ -39,6 +40,7 @@ mod derive;
 mod deriving;
 mod edition_panic;
 mod env;
+mod errors;
 mod format;
 mod format_foreign;
 mod global_allocator;