Replace __cplusplus comparisons and dialect __has_feature checks with TEST_STD_VER.

This is a huge cleanup that helps make the libc++ test suite more portable.
Patch from STL@microsoft.com. Thanks STL!


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@272716 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/iterators/iterator.range/begin-end.pass.cpp

@@ -15,7 +15,9 @@
 // template <class E> reverse_iterator<const E*> rbegin(initializer_list<E> il);
 // template <class E> reverse_iterator<const E*> rend(initializer_list<E> il);
 
-#if __cplusplus >= 201103L
+#include "test_macros.h"
+
+#if TEST_STD_VER >= 11
 #include <iterator>
 #include <cassert>
 #include <vector>