Implement LWG Issue: 2280. begin/end for arrays should be constexpr and noexcept, plus a drive-by fix for cbegin/cend suggested by Peter Sommerlad.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@201703 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/iterator b/include/iterator
index c6dd033..28a946c 100644
--- a/include/iterator
+++ b/include/iterator
@@ -1386,7 +1386,7 @@
 }
 
 template <class _Tp, size_t _Np>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _Tp*
 begin(_Tp (&__array)[_Np])
 {
@@ -1394,7 +1394,7 @@
 }
 
 template <class _Tp, size_t _Np>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 _Tp*
 end(_Tp (&__array)[_Np])
 {
@@ -1466,17 +1466,17 @@
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 auto cbegin(const _Cp& __c) -> decltype(begin(__c))
 {
-    return _VSTD::begin(__c);
+    return begin(__c);
 }
 
 template <class _Cp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 auto cend(const _Cp& __c) -> decltype(end(__c))
 {
-    return _VSTD::end(__c);
+    return end(__c);
 }
 
 template <class _Cp>