C++: add Class::isStandardLayout()

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

@@ -418,6 +418,12 @@ class Class extends UserType {
    */
   predicate isPOD() { is_pod_class(underlyingElement(this)) }
 
+  /**
+   * Holds if this class is a standard-layout class [N4140 9(7)]. Also holds
+   * for structs in C programs.
+   */
+  predicate isStandardLayout() { is_standard_layout_class(underlyingElement(this)) }
+
   /**
    * Holds if this class is abstract, in other words whether it declares one
    * or more pure virtual member functions.

cpp/ql/src/semmlecode.cpp.dbscheme

@@ -691,6 +691,7 @@ usertype_uuid(
 );
 
 is_pod_class(unique int id: @usertype ref);
+is_standard_layout_class(unique int id: @usertype ref);
 
 is_complete(unique int id: @usertype ref);