[committed] libstdc++: Fix preprocessor condition for inline variables

[Jonathan Wakely <jwakely@redhat.com>]

Tested x86_64-linux. Pushed to trunk.

-- >8 --

Although variable templates are valid in C++14, inline ones aren't.
These are only used in C++17 (or later) code, so they don't need to be
defined for C++14.

libstdc++-v3/ChangeLog:

	* include/bits/chrono.h (__is_duration_v, __is_time_point_v):
	Only define for C++17 and later.
---
 libstdc++-v3/include/bits/chrono.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/chrono.h b/libstdc++-v3/include/bits/chrono.h
index b2e4f4c33a8..fb99fe5eed7 100644
--- a/libstdc++-v3/include/bits/chrono.h
+++ b/libstdc++-v3/include/bits/chrono.h
@@ -244,7 +244,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       using __disable_if_is_duration
 	= typename enable_if<!__is_duration<_Tp>::value, _Tp>::type;
 
-#if __cpp_variable_templates
+#if __cplusplus >= 201703L
     template<typename _Tp>
       inline constexpr bool __is_duration_v = false;
     template<typename _Rep, typename _Period>
-- 
2.39.2