[libSyntax] Minor ref-counting improvements

Author: ahoppen

lib/SyntaxParse/RawSyntaxTokenCache.h

@@ -44,7 +44,7 @@ class RawSyntaxCacheNode : public llvm::FoldingSetNode {
       : Obj(Obj), IDRef(IDRef) {}
 
   /// Retrieve assciated RawSyntax.
-  RC<syntax::RawSyntax> get() { return Obj; }
+  const RC<syntax::RawSyntax> &get() { return Obj; }
 
   // Only allow allocation of Node using the allocator in SyntaxArena.
   void *operator new(size_t Bytes, RC<syntax::SyntaxArena> &Arena,