Compute proc_macros in resolutions.

compiler/rustc_middle/src/ty/mod.rs

@@ -134,6 +134,9 @@ pub struct ResolverOutputs {
     pub extern_prelude: FxHashMap<Symbol, bool>,
     pub main_def: Option<MainDefinition>,
     pub trait_impls: BTreeMap<DefId, Vec<LocalDefId>>,
+    /// A list of proc macro LocalDefIds, written out in the order in which
+    /// they are declared in the static array generated by proc_macro_harness.
+    pub proc_macros: Vec<LocalDefId>,
 }
 
 #[derive(Clone, Copy, Debug)]