C++: Make getUnderlyingType 'nomagic'.

Author: geoffw0

cpp/ql/lib/semmle/code/cpp/Type.qll

@@ -94,7 +94,7 @@ class Type extends Locatable, @type {
    * The result of this predicate will be the type itself, except in the case of a TypedefType or a Decltype,
    * in which case the result will be type which results from (possibly recursively) resolving typedefs.
    */
-  Type getUnderlyingType() { result = this }
+  pragma[nomagic] Type getUnderlyingType() { result = this }
 
   /**
    * Gets this type after specifiers have been deeply stripped and typedefs have been resolved.