Add file with warning for backward comptibility. Should be removed after 2.4

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51693 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/iterator

@@ -0,0 +1,36 @@
+//===-- llvm/ADT/iterator - Portable wrapper around <iterator> --*- C++ -*-===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file provides a wrapper around the mysterious <iterator> header file.
+// In GCC 2.95.3, the file defines a bidirectional_iterator class (and other
+// friends), instead of the standard iterator class.  In GCC 3.1, the
+// bidirectional_iterator class got moved out and the new, standards compliant,
+// iterator<> class was added.  Because there is nothing that we can do to get
+// correct behavior on both compilers, we have this header with #ifdef's.  Gross
+// huh?
+//
+// By #includ'ing this file, you get the contents of <iterator> plus the
+// following classes in the global namespace:
+//
+//   1. bidirectional_iterator
+//   2. forward_iterator
+//
+// The #if directives' expressions are filled in by Autoconf.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ADT_ITERATOR
+#define LLVM_ADT_ITERATOR
+
+#warning This files includes old 'llvm/ADT/iterator' file, which was replaced  \
+by 'llvm/ADT/iterator.h'. Please consider upgrading the source.
+
+#include "llvm/ADT/iterator.h"
+
+#endif // LLVM_ADT_ITERATOR