[gcc r16-820] libstdc++: Fix PSTL test iterators

[Jonathan Wakely]

https://gcc.gnu.org/g:c0a2526f099dfa52df5daa1432ff583ae6af0d5f

commit r16-820-gc0a2526f099dfa52df5daa1432ff583ae6af0d5f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue May 20 13:18:52 2025 +0100

    libstdc++: Fix PSTL test iterators
    
    These were fixed upstream by:
    https://github.com/uxlfoundation/oneDPL/pull/534
    https://github.com/uxlfoundation/oneDPL/pull/546
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/util/pstl/test_utils.h (ForwardIterator::operator++):
            Fix return type.
            (BidirectionalIterator::operator++): Likewise.
            (BidirectionalIterator::operator--): Likewise.

Diff:
---
 libstdc++-v3/testsuite/util/pstl/test_utils.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/testsuite/util/pstl/test_utils.h b/libstdc++-v3/testsuite/util/pstl/test_utils.h
index 55b510098a04..9c61a7145f59 100644
--- a/libstdc++-v3/testsuite/util/pstl/test_utils.h
+++ b/libstdc++-v3/testsuite/util/pstl/test_utils.h
@@ -154,7 +154,7 @@ class ForwardIterator
     explicit ForwardIterator(Iterator i) : my_iterator(i) {}
     reference operator*() const { return *my_iterator; }
     Iterator operator->() const { return my_iterator; }
-    ForwardIterator
+    ForwardIterator&
     operator++()
     {
         ++my_iterator;
@@ -194,13 +194,13 @@ class BidirectionalIterator : public ForwardIterator<Iterator, IteratorTag>
     explicit BidirectionalIterator(Iterator i) : base_type(i) {}
     BidirectionalIterator(const base_type& i) : base_type(i.iterator()) {}
 
-    BidirectionalIterator
+    BidirectionalIterator&
     operator++()
     {
         ++base_type::my_iterator;
         return *this;
     }
-    BidirectionalIterator
+    BidirectionalIterator&
     operator--()
     {
         --base_type::my_iterator;