Issue #25092: Fix datetime.strftime() failure when errno was already set to EINVAL.

Misc/NEWS

@@ -18,6 +18,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #25092: Fix datetime.strftime() failure when errno was already set to
+  EINVAL.
+
 - Issue #23517: Fix rounding in fromtimestamp() and utcfromtimestamp() methods
   of datetime.datetime: microseconds are now rounded to nearest with ties
   going to nearest even integer (ROUND_HALF_EVEN), instead of being rounding

Modules/timemodule.c

@@ -653,6 +653,9 @@ time_strftime(PyObject *self, PyObject *args)
             PyErr_NoMemory();
             break;
         }
+#if defined _MSC_VER && _MSC_VER >= 1400 && defined(__STDC_SECURE_LIB__)
+        errno = 0;
+#endif
         _Py_BEGIN_SUPPRESS_IPH
         buflen = format_time(outbuf, i, fmt, &buf);
         _Py_END_SUPPRESS_IPH