Add chrono.cpp definitions to support the creation of time point from iso string in cdt

src/chrono.cpp

@@ -0,0 +1,17 @@
+#include "chrono"
+#include "cerrno"
+#include <time.h>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace chrono
+{
+   system_clock::time_point
+
+   system_clock::from_time_t(time_t t) _NOEXCEPT
+   {
+      return system_clock::time_point(seconds(t));
+   }
+} // ns chrono
+
+_LIBCPP_END_NAMESPACE_STD