[committed] libstdc++: Use appropriate feature test macro for std::byte

[Jonathan Wakely]

Tested x86_64-linux. Pushed to trunk.

-- >8 --

libstdc++-v3/ChangeLog:

        * include/bits/cpp_type_traits.h (__is_byte<byte>): Guard with
        __glibcxx_byte macro instead of checking __cplusplus.
---
 libstdc++-v3/include/bits/cpp_type_traits.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h 
b/libstdc++-v3/include/bits/cpp_type_traits.h
index 19bf1edf647..060652afb18 100644
--- a/libstdc++-v3/include/bits/cpp_type_traits.h
+++ b/libstdc++-v3/include/bits/cpp_type_traits.h
@@ -414,7 +414,7 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
       typedef __true_type __type;
     };
 
-#if __cplusplus >= 201703L
+#ifdef __glibcxx_byte // C++ >= 17
   enum class byte : unsigned char;
 
   template<>
-- 
2.46.2