[gcc r12-4521] libstdc++: Implement LWG 3580 change to ranges::iota_view

[Patrick Palka]

https://gcc.gnu.org/g:5566f3c6b46cf053ae4b918513e318561b7af053

commit r12-4521-g5566f3c6b46cf053ae4b918513e318561b7af053
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Oct 19 18:07:19 2021 -0400

    libstdc++: Implement LWG 3580 change to ranges::iota_view
    
    libstdc++-v3/ChangeLog:
    
            * include/std/ranges (iota_view::_Iterator::operator+): Adjust
            definition as per LWG 3580.
            (iota_view::_Iterator::operator-): Likewise.

Diff:
---
 libstdc++-v3/include/std/ranges | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index c3a6dbab6fd..273699aa790 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -497,7 +497,10 @@ namespace ranges
 	friend constexpr _Iterator
 	operator+(_Iterator __i, difference_type __n)
 	  requires __detail::__advanceable<_Winc>
-	{ return __i += __n; }
+	{
+	  __i += __n;
+	  return __i;
+	}
 
 	friend constexpr _Iterator
 	operator+(difference_type __n, _Iterator __i)
@@ -507,7 +510,10 @@ namespace ranges
 	friend constexpr _Iterator
 	operator-(_Iterator __i, difference_type __n)
 	  requires __detail::__advanceable<_Winc>
-	{ return __i -= __n; }
+	{
+	  __i -= __n;
+	  return __i;
+	}
 
 	friend constexpr difference_type
 	operator-(const _Iterator& __x, const _Iterator& __y)