[PATCH] Update value of __cpp_lib_chrono feature-test macro

[Jonathan Wakely]

Dinka Ranns contributed this feature back in February, but the SD-6
feature-test macro now has a new value to indicate support for this,
so let's update it.

        * include/std/chrono (__cpp_lib_chrono): Update macro value to
        indicate support for P0505R0.
        * testsuite/20_util/duration/arithmetic/constexpr_c++17.cc: Check
        for updated macro.

Tested powerpc64le-linux, committed to trunk and gcc-7-branch.



commit 8a7bf24c72d1373571d8f61d8078c874425c8256
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri Oct 20 19:53:24 2017 +0100

    Update value of __cpp_lib_chrono feature-test macro
    
            * include/std/chrono (__cpp_lib_chrono): Update macro value to
            indicate support for P0505R0.
            * testsuite/20_util/duration/arithmetic/constexpr_c++17.cc: Check
            for updated macro.

diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
index fc058fcd8d8..9491508e637 100644
--- a/libstdc++-v3/include/std/chrono
+++ b/libstdc++-v3/include/std/chrono
@@ -214,8 +214,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         treat_as_floating_point<_Rep>::value;
 #endif // C++17
 
-#if __cplusplus > 201402L
-# define __cpp_lib_chrono 201510
+#if __cplusplus >= 201703L
+# define __cpp_lib_chrono 201611
 
     template<typename _ToDur, typename _Rep, typename _Period>
       constexpr __enable_if_is_duration<_ToDur>
diff --git 
a/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr_c++17.cc 
b/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr_c++17.cc
index 438d50afddf..0ba1b8cc706 100644
--- a/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr_c++17.cc
+++ b/libstdc++-v3/testsuite/20_util/duration/arithmetic/constexpr_c++17.cc
@@ -20,6 +20,13 @@
 
 #include <chrono>
 #include <testsuite_common_types.h>
+
+#ifndef __cpp_lib_chrono
+# error "Feature-test macro for constexpr <chrono> missing"
+#elif __cpp_lib_chrono != 201611
+# error "Feature-test macro for constexpr <chrono> has wrong value"
+#endif
+
 constexpr auto test_operators()
 {
   std::chrono::nanoseconds d1 { 1 };