Fixed MacOS build

The LLVM STL implementation does not recognize "typedef void iterator_traits"
as dummy declaration. It will fall back to an empty traits struct.
Using the default "forward_iterator_tag" for the iterator_traits solves
this compile issue.

src/db/db/dbArray.h

@@ -1208,7 +1208,7 @@ struct array_iterator
   typedef void pointer_type;
   typedef void difference_type;
   typedef void pointer;
-  typedef void iterator_category;
+  typedef std::forward_iterator_tag iterator_category;
 
   /**
    *  @brief The default constructor

src/db/db/gsiDeclDbLayoutQuery.cc

@@ -70,7 +70,7 @@ struct LayoutQueryIteratorWrapper
 {
   typedef db::LayoutQueryIterator &reference;
   //  Dummy declarations
-  typedef void iterator_category;
+  typedef std::forward_iterator_tag iterator_category;
   typedef void value_type;
   typedef void difference_type;
   typedef void pointer;

src/db/db/gsiDeclDbShape.cc

@@ -954,7 +954,7 @@ struct ConvertingIteratorWrapper
   typedef T value_type;
   typedef T reference;
   typedef void pointer;
-  typedef void iterator_category;
+  typedef std::forward_iterator_tag iterator_category;
 
   ConvertingIteratorWrapper (double dbu, const I &b, const I &e)
     : m_b (b), m_e (e), m_dbu (dbu)
@@ -989,7 +989,7 @@ struct ConvertingFreeIteratorWrapper
   typedef T value_type;
   typedef T reference;
   typedef void pointer;
-  typedef void iterator_category;
+  typedef std::forward_iterator_tag iterator_category;
 
   ConvertingFreeIteratorWrapper (double dbu, const I &b)
     : m_b (b), m_dbu (dbu)

src/gsi/gsi/gsiIterators.h

@@ -28,6 +28,8 @@
 #include "tlTypeTraits.h"
 #include "gsiSerialisation.h"
 
+#include <iterator>
+
 //  For a comprehensive documentation see gsi.h
 
 namespace gsi

src/laybasic/laybasic/gsiDeclLayLayoutView.cc

@@ -320,7 +320,7 @@ namespace {
     typedef lay::LayerPropertiesNodeRef value_type;
     typedef lay::LayerPropertiesNodeRef reference;
     //  Dummy declarations required for std::iterator_traits
-    typedef void iterator_category;
+    typedef std::forward_iterator_tag iterator_category;
     typedef void difference_type;
     typedef void pointer;