Zhang Xiongpang: Add definitions for const data members. Fixes http://llvm.org/bugs/show_bug.cgi?id=14585.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@170026 91177308-0d34-0410-b5e6-96231b3b80d8

src/chrono.cpp

@@ -24,6 +24,8 @@ namespace chrono
 
 // system_clock
 
+const bool system_clock::is_steady;
+
 system_clock::time_point
 system_clock::now() _NOEXCEPT
 {
@@ -46,6 +48,8 @@ system_clock::from_time_t(time_t t) _NOEXCEPT
 
 // steady_clock
 
+const bool steady_clock::is_steady;
+
 #if __APPLE__
 //   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
 //   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom