C++: One more speedup, address review.

cpp/ql/src/semmle/code/cpp/Element.qll

@@ -66,7 +66,7 @@ class ElementBase extends @element {
    * `BinaryOperation` is not.
    *
    * This predicate can have multiple results if multiple primary classes match.
-   * For some elements, this predicate may not exist.
+   * For some elements, this predicate may not have a result.
    */
   string getAPrimaryQlClass() { none() }
 }

cpp/ql/src/semmle/code/cpp/PrintAST.qll

@@ -237,11 +237,11 @@ class PrintASTNode extends TPrintASTNode {
 
 private class PrintableElementBase extends ElementBase {
   PrintableElementBase() {
-    shouldPrintFunction(getEnclosingFunction(this))
+    exists(TASTNode(this))
+    or
+    exists(TDeclarationEntryNode(_, this))
     or
     this instanceof Type
-    or
-    this instanceof DeclarationEntry
   }
 
   pragma[noinline]