[gcc r12-4590] libstdc++: Implement LWG 3595 changes to common_iterator

[gcc r12-4590] libstdc++: Implement LWG 3595 changes to common_iterator

[Patrick Palka]

https://gcc.gnu.org/g:1556e447c0fee5c77ccd9bda243d5281e10e895b

commit r12-4590-g1556e447c0fee5c77ccd9bda243d5281e10e895b
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.

Diff:
---
 libstdc++-v3/include/bits/stl_iterator.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 8afd6756613..0090b2d598f 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1821,13 +1821,14 @@ _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>*
+      constexpr const iter_value_t<_It>*
       operator->() const noexcept
       { return std::__addressof(_M_keep); }
     };
@@ -1836,13 +1837,14 @@ _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>&
+      constexpr const iter_value_t<_It>&
       operator*() const noexcept
       { return _M_keep; }
     };