First part of P1227R2 - change span over to use 'size_t' instead of 'ptrdiff_t'. Reviewed as https://reviews.llvm.org/D58639.

llvm-svn: 354936
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 7ad06a9319fdd54a890f75026049e3e4bcfa061e
diff --git a/include/iterator b/include/iterator
index 242f188..ce0be3d 100644
--- a/include/iterator
+++ b/include/iterator
@@ -1442,7 +1442,7 @@
     template <class _Up> friend class __wrap_iter;
     template <class _CharT, class _Traits, class _Alloc> friend class basic_string;
     template <class _Tp, class _Alloc> friend class _LIBCPP_TEMPLATE_VIS vector;
-    template <class _Tp, ptrdiff_t> friend class _LIBCPP_TEMPLATE_VIS span;
+    template <class _Tp, size_t> friend class _LIBCPP_TEMPLATE_VIS span;
 
     template <class _Iter1, class _Iter2>
     _LIBCPP_CONSTEXPR_IF_NODEBUG friend