[gcc r13-3889] libstdc++: Fix test that uses C++17 variable template in C++14

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:56d2222c58be78d5125bd8a1069364f0f4b2baa2

commit r13-3889-g56d2222c58be78d5125bd8a1069364f0f4b2baa2
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Nov 10 14:04:07 2022 +0000

    libstdc++: Fix test that uses C++17 variable template in C++14
    
    This test fails if run with -std=gnu++14 because it should be using
    is_convertible instead of is_convertible_v.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/experimental/propagate_const/observers/107525.cc:
            Use type trait instead of C++17 variable template.

Diff:
---
 .../testsuite/experimental/propagate_const/observers/107525.cc        | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/testsuite/experimental/propagate_const/observers/107525.cc b/libstdc++-v3/testsuite/experimental/propagate_const/observers/107525.cc
index e7ecff73c1a..37e970c3af4 100644
--- a/libstdc++-v3/testsuite/experimental/propagate_const/observers/107525.cc
+++ b/libstdc++-v3/testsuite/experimental/propagate_const/observers/107525.cc
@@ -32,10 +32,10 @@ test_const_conversion()
     operator const int*() const = delete;
   };
 
-  static_assert(!std::is_convertible_v<const X, const int*>,
+  static_assert(!std::is_convertible<const X, const int*>::value,
 		"Cannot convert const X to const int*");
   // So should not be able to convert const propagate_const<X> to const int*.
-  static_assert(!std::is_convertible_v<const propagate_const<X>, const int*>,
+  static_assert(!std::is_convertible<const propagate_const<X>, const int*>::value,
 		"So should not be able to convert const propagate_const<X> to "
 		"const int* (although this is not what LFTSv3 says)");
 }