[gcc r10-10578] libstdc++: Use __cpp_lib_concepts in std::reverse_iterator [PR104098]

[gcc r10-10578] libstdc++: Use __cpp_lib_concepts in std::reverse_iterator [PR104098]

[Jonathan Wakely]

https://gcc.gnu.org/g:5c8f58be95d666e08221447d43d84782e1e6fb95

commit r10-10578-g5c8f58be95d666e08221447d43d84782e1e6fb95
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Jan 18 15:34:24 2022 +0000

    libstdc++: Use __cpp_lib_concepts in std::reverse_iterator [PR104098]
    
    We should not assume that std::iter_value_t etc. are defined
    unconditionally for C++20 mode.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/104098
            * include/bits/stl_iterator.h (reverse_iterator): Check
            __cpp_lib_concepts instead of __cplusplus.
    
    (cherry picked from commit e13e95bd274148a825bc9527efac49e99080dd64)

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

diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 85e58973ac6..215822581a3 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -92,7 +92,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    * @{
    */
 
-#if __cplusplus > 201703L && __cpp_lib_concepts
+#if __cpp_lib_concepts
   namespace __detail
   {
     // Weaken iterator_category _Cat to _Limit if it is derived from that,
@@ -138,7 +138,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     public:
       typedef _Iterator					iterator_type;
       typedef typename __traits_type::pointer		pointer;
-#if __cplusplus <= 201703L
+#if ! __cpp_lib_concepts
       typedef typename __traits_type::difference_type	difference_type;
       typedef typename __traits_type::reference		reference;
 #else