libstdc++: Implement LWG 3546 changes to common_iterator

libstdc++-v3/ChangeLog:

	* include/bits/stl_iterator.h
	(__detail::__common_iter_use_postfix_proxy): Add
	move_constructible constraint as per LWG 3546.
	(common_iterator::__postfix_proxy): Adjust initializer of
	_M_keep as per LWG 3546.

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 6ec046b597bb921950e83cc2703e8554a9f8458c..7fe727d8093f3ce24121d5268c4639ce00304ab0 100644 (file)
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1672,7 +1672,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _It>
       concept __common_iter_use_postfix_proxy
        = (!requires (_It& __i) { { *__i++ } -> __can_reference; })
-         && constructible_from<iter_value_t<_It>, iter_reference_t<_It>>;
+         && constructible_from<iter_value_t<_It>, iter_reference_t<_It>>
+         && move_constructible<iter_value_t<_It>>;
   } // namespace __detail
 
   /// An iterator/sentinel adaptor for representing a non-common range.
@@ -1715,7 +1716,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       iter_value_t<_It> _M_keep;
 
       __postfix_proxy(iter_reference_t<_It>&& __x)
-      : _M_keep(std::move(__x)) { }
+      : _M_keep(std::forward<iter_reference_t<_It>>(__x)) { }
 
       friend class common_iterator;