Always cache macro expansions' root node in Semantics

Previously some expansions were not cached, but were cached in the expansion cache, which caused panics when later queries tried to lookup the node from the expansion cache.

crates/hir-expand/src/builtin.rs

@@ -1,6 +1,6 @@
 //! Builtin macros and attributes
 #[macro_use]
-mod quote;
+pub mod quote;
 
 mod attr_macro;
 mod derive_macro;