Make the query comment into a doc comment

Author: Xanewok

src/librustc/ty/query/mod.rs

@@ -476,7 +476,8 @@ define_queries! { <'tcx>
 
         [] fn foreign_modules: ForeignModules(CrateNum) -> Lrc<Vec<ForeignModule>>,
 
-        // For a library crate, this is always none
+        /// Identifies the entry-point (e.g. the `main` function) for a given
+        /// crate, returning `None` if there is no entry point (such as for library crates).
         [] fn entry_fn: EntryFn(CrateNum) -> Option<(DefId, EntryFnType)>,
         [] fn plugin_registrar_fn: PluginRegistrarFn(CrateNum) -> Option<DefId>,
         [] fn proc_macro_decls_static: ProcMacroDeclsStatic(CrateNum) -> Option<DefId>,