systemc: replace the deprecated std::iterator

std::iterator is deprecated in c++17. We can just declare the
required types for iterator traits directly without the helper.

Change-Id: I789e2c2b13e56cc391527686109df8b779474d09
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66351
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/systemc/ext/utils/sc_vector.hh

@@ -49,6 +49,7 @@
 
 #include <stdint.h>
 
+#include <cstddef>
 #include <exception>
 #include <iterator>
 #include <vector>
@@ -259,10 +260,7 @@ class sc_member_access
 
 template <typename Element,
           typename AccessPolicy=sc_direct_access<Element> >
-class sc_vector_iter :
-        public std::iterator<std::random_access_iterator_tag,
-                             typename AccessPolicy::Type>,
-        private AccessPolicy
+class sc_vector_iter : private AccessPolicy
 {
   private:
     typedef Element ElementType;
@@ -282,8 +280,6 @@ class sc_vector_iter :
     template <typename, typename>
     friend class sc_vector_iter;
 
-    typedef std::iterator<std::random_access_iterator_tag, AccessType>
-        BaseType;
     typedef sc_vector_iter ThisType;
     typedef sc_vector<PlainType> VectorType;
     typedef std::vector<void *> StorageType;
@@ -315,9 +311,11 @@ class sc_vector_iter :
     // Conforms to Random Access Iterator category.
     // See ISO/IEC 14882:2003(E), 24.1 [lib.iterator.requirements]
 
-    typedef typename BaseType::difference_type difference_type;
-    typedef typename BaseType::reference reference;
-    typedef typename BaseType::pointer pointer;
+    using difference_type = std::ptrdiff_t;
+    using value_type = typename AccessPolicy::Type;
+    using reference = typename AccessPolicy::Type &;
+    using pointer = typename AccessPolicy::Type *;
+    using iterator_category = std::random_access_iterator_tag;
 
     sc_vector_iter() : Policy(), it_() {}