Only process a base type as a class when it is a class.

src/Generator/Passes/DuplicatedNamesCheckerPass.cs

@@ -19,6 +19,7 @@ namespace Cxxi.Passes
             names.Clear();
 
             foreach (var baseClass in @class.Bases)
+                if (baseClass.IsClass)
                     ProcessClass(baseClass.Class);
 
             CheckDuplicates(@class.Fields);