Work around ABI break caused by C++17 inline variables.

llvm-svn: 274403
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: d3a1ed814b8fa0af7277fb02a6037223aec98371
diff --git a/src/chrono.cpp b/src/chrono.cpp
index 62149fb..14b848b 100644
--- a/src/chrono.cpp
+++ b/src/chrono.cpp
@@ -6,7 +6,7 @@
 // Source Licenses. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
-
+#define _LIBCPP_BUILDING_CHRONO
 #include "chrono"
 #include "cerrno"        // errno
 #include "system_error"  // __throw_system_error
@@ -32,6 +32,9 @@
 // system_clock
 
 const bool system_clock::is_steady;
+// Make is_steady non-discardable in C++17
+// See PR28395 (https://llvm.org/bugs/show_bug.cgi?id=28395)
+static const bool& __is_steady_force_use1 __attribute__((used)) = system_clock::is_steady;
 
 system_clock::time_point
 system_clock::now() _NOEXCEPT
@@ -68,6 +71,10 @@
 //  instead.
 
 const bool steady_clock::is_steady;
+// Make is_steady non-discardable in C++17
+// See PR28395 (https://llvm.org/bugs/show_bug.cgi?id=28395)
+static const bool& __is_steady_force_use2 __attribute__((used)) = steady_clock::is_steady;
+
 
 #ifdef CLOCK_MONOTONIC