Do not check for duplicates when handling preprocessed entities.

Even though they share the same original ptr to clang's PreprocessedEntity, they can still have different locations so we need to duplicate them when converting the AST.

src/Core/Parser/ASTConverter.cs

@@ -599,6 +599,7 @@ namespace CppSharp
 
             // Check if the declaration was already handled and return its
             // existing instance.
+            if (CheckForDuplicates(decl))
                 if (Declarations.ContainsKey(originalPtr))
                     return Declarations[originalPtr];
 
@@ -674,10 +675,16 @@ namespace CppSharp
             }
         }
 
+        bool CheckForDuplicates(Declaration decl)
+        {
+            return !(decl is PreprocessedEntity);
+        }
+
         void VisitDeclaration(Declaration decl, AST.Declaration _decl)
         {
             var originalPtr = new IntPtr(decl.OriginalPtr);
 
+            if (CheckForDuplicates(decl))
                 if (Declarations.ContainsKey(originalPtr))
                     throw new NotSupportedException("Duplicate declaration processed");