commit d78a141b86aca5a1265ec2df96428ef387492a1f
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Oct 23 16:19:28 2019 +0100

    Only qualify function as constexpr for C++14 and later
    
    This helper function is not a valid constexpr function in C++11, so
    should only be marked constexpr for C++14 and later.
    
            * include/debug/helper_functions.h (__valid_range): Change
            _GLIBCXX_CONSTEXPR to _GLIBCXX14_CONSTEXPR.

diff --git a/libstdc++-v3/include/debug/helper_functions.h b/libstdc++-v3/include/debug/helper_functions.h
index 5a920bb9a6f..c3e7478f649 100644
--- a/libstdc++-v3/include/debug/helper_functions.h
+++ b/libstdc++-v3/include/debug/helper_functions.h
@@ -221,7 +221,7 @@ namespace __gnu_debug
 #endif
 
   template<typename _InputIterator>
-    _GLIBCXX_CONSTEXPR
+    _GLIBCXX14_CONSTEXPR
     inline bool
     __valid_range(_InputIterator __first, _InputIterator __last)
     {