[gcc r11-9821] libstdc++: Implement LWG 3595 changes to common_iterator

[gcc r11-9821] libstdc++: Implement LWG 3595 changes to common_iterator

[Patrick Palka]

https://gcc.gnu.org/g:813425498f41ab631fb1d9f4dc477cf74e3cc4a8

commit r11-9821-g813425498f41ab631fb1d9f4dc477cf74e3cc4a8
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Oct 20 21:43:42 2021 -0400

    libstdc++: Implement LWG 3595 changes to common_iterator
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/stl_iterator.h (common_iterator::__arrow_proxy):
            Make fully constexpr as per LWG 3595.
            (common_iterator::__postfix_proxy): Likewise.
    
    (cherry picked from commit 1556e447c0fee5c77ccd9bda243d5281e10e895b)

Diff:
---
 libstdc++-v3/include/bits/stl_iterator.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 79e9959fc58..beeb4ef4c8a 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1711,14 +1711,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       iter_value_t<_It> _M_keep;
 
+      constexpr
       __arrow_proxy(iter_reference_t<_It>&& __x)
       : _M_keep(std::move(__x)) { }
 
       friend class common_iterator;
 
     public:
-      const iter_value_t<_It>*
-      operator->() const
+      constexpr const iter_value_t<_It>*
+      operator->() const noexcept
       { return std::__addressof(_M_keep); }
     };
 
@@ -1726,14 +1727,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       iter_value_t<_It> _M_keep;
 
+      constexpr
       __postfix_proxy(iter_reference_t<_It>&& __x)
       : _M_keep(std::forward<iter_reference_t<_It>>(__x)) { }
 
       friend class common_iterator;
 
     public:
-      const iter_value_t<_It>&
-      operator*() const
+      constexpr const iter_value_t<_It>&
+      operator*() const noexcept
       { return _M_keep; }
     };