Extend https://github.com/imageworks/Field3D/commit/02f990403620cc890f2075a7b7fa4bd661390041 to cover old OS
diff --git export/DenseField.h export/DenseField.h
index 740a663..3e3c693 100644
--- export/DenseField.h
+++ export/DenseField.h
@@ -257,7 +257,7 @@ template <class Data_T>
 class DenseField<Data_T>::const_iterator
 {
 public:
-#if defined(WIN32) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
+#if defined(WIN32) || defined(__APPLE__)
   typedef std::forward_iterator_tag iterator_category;
   typedef Data_T value_type;
   typedef ptrdiff_t difference_type;
@@ -352,7 +352,7 @@ template <class Data_T>
 class DenseField<Data_T>::iterator
 {
 public:
-#if defined(WIN32) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
+#if defined(WIN32) || defined(__APPLE__)
   typedef std::forward_iterator_tag iterator_category;
   typedef Data_T value_type;
   typedef ptrdiff_t difference_type;
diff --git export/Field.h export/Field.h
index 51fd35d..aab5fa8 100644
--- export/Field.h
+++ export/Field.h
@@ -492,7 +492,7 @@ class Field<Data_T>::const_iterator
 {
 
 public:
-#if defined(WIN32) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
+#if defined(WIN32) || defined(__APPLE__)
   typedef std::forward_iterator_tag iterator_category;
   typedef Data_T value_type;
   typedef ptrdiff_t difference_type;
@@ -703,7 +703,7 @@ template <class Data_T>
 class WritableField<Data_T>::iterator
 {
 public:
-#if defined(WIN32) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
+#if defined(WIN32) || defined(__APPLE__)
   typedef std::forward_iterator_tag iterator_category;
   typedef Data_T value_type;
   typedef ptrdiff_t difference_type;
diff --git export/SparseField.h export/SparseField.h
index e8ac64b..4444bc9 100644
--- export/SparseField.h
+++ export/SparseField.h
@@ -885,7 +885,7 @@ template <class Data_T>
 class SparseField<Data_T>::const_iterator
 {
  public:
-#if defined(WIN32) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
+#if defined(WIN32) || defined(__APPLE__)
   typedef std::forward_iterator_tag iterator_category;
   typedef Data_T value_type;
   typedef ptrdiff_t difference_type;
@@ -1067,7 +1067,7 @@ template <class Data_T>
 class SparseField<Data_T>::iterator
 {
  public:
-#if defined(WIN32) || __MAC_OS_X_VERSION_MIN_REQUIRED >= 1090
+#if defined(WIN32) || defined(__APPLE__)
   typedef std::forward_iterator_tag iterator_category;
   typedef Data_T value_type;
   typedef ptrdiff_t difference_type;