Accommodating environments that define __STDC_WANT_LIB_EXT1__ even if __STDC_LIB_EXT1__ is not defined by the implementation. (#3151)

Follow-on to PR #3129.

Author: rwgk

include/pybind11/chrono.h

@@ -101,7 +101,7 @@ template <typename type> class duration_caster {
 };
 
 inline std::tm *localtime_thread_safe(const std::time_t *time, std::tm *buf) {
-#if defined(__STDC_WANT_LIB_EXT1__) || defined(_MSC_VER)
+#if (defined(__STDC_LIB_EXT1__) && defined(__STDC_WANT_LIB_EXT1__)) || defined(_MSC_VER)
     if (localtime_s(buf, time))
         return nullptr;
     return buf;