C++: Support __is_aggregate builtin

Fix some whitespace issues while here.

cpp/ql/lib/semmle/code/cpp/exprs/BuiltInOperations.qll

@@ -991,3 +991,17 @@ class BuiltInComplexOperation extends BuiltInOperation, @builtincomplex {
   /** Gets the operand corresponding to the imaginary part of the complex number. */
   Expr getImaginaryOperand() { this.hasChild(result, 1) }
 }
+
+/**
+ * A C++ `__is_aggregate` built-in operation (used by some implementations of the
+ * `<type_traits>` header).
+ *
+ * Returns `true` if the type has is an aggregate type.
+ * ```
+ * std::integral_constant<bool, __is_aggregate(_Tp)> ia;
+ * ``` */
+class BuiltInOperationIsAggregate extends BuiltInOperation, @isaggregate {
+  override string toString() { result = "__is_aggregate" }
+
+  override string getAPrimaryQlClass() { result = "BuiltInOperationIsAggregate" }
+}

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -1651,6 +1651,7 @@ case @expr.kind of
 | 328 = @co_yield
 | 329 = @temp_init
 | 330 = @isassignable
+| 331 = @isaggregate
 ;
 
 @var_args_expr = @vastartexpr
@@ -1713,6 +1714,7 @@ case @expr.kind of
             | @builtinchooseexpr
             | @builtincomplex
             | @isassignable
+            | @isaggregate
             ;
 
 new_allocated_type(

cpp/ql/test/library-tests/builtins/type_traits/expr.expected

@@ -305,3 +305,7 @@
 | ms.cpp:260:29:260:57 | __is_assignable | a_struct,int | 0 |
 | ms.cpp:260:29:260:57 | a_struct |  | <none> |
 | ms.cpp:260:29:260:57 | int |  | <none> |
+| ms.cpp:262:28:262:51 | __is_aggregate | a_struct | 1 |
+| ms.cpp:262:28:262:51 | a_struct |  | <none> |
+| ms.cpp:263:28:263:46 | __is_aggregate | int | 0 |
+| ms.cpp:263:28:263:46 | int |  | <none> |

cpp/ql/test/library-tests/builtins/type_traits/ms.cpp

@@ -258,4 +258,7 @@ void f(void) {
     bool b_is_assignable1 = __is_assignable(a_struct,a_struct);
     bool b_is_assignable2 = __is_assignable(a_struct,empty);
     bool b_is_assignable3 = __is_assignable(a_struct,int);
+
+    bool b_is_aggregate1 = __is_aggregate(a_struct);
+    bool b_is_aggregate2 = __is_aggregate(int);
 }