Use PyOS_snprintf for better portability.

Modules/timemodule.c

@@ -605,7 +605,7 @@ _asctime(struct tm *timeptr)
     char buf[20]; /* 'Sun Sep 16 01:03:52\0' */
     int n;
 
-    n = snprintf(buf, sizeof(buf), "%.3s %.3s%3d %.2d:%.2d:%.2d",
+    n = PyOS_snprintf(buf, sizeof(buf), "%.3s %.3s%3d %.2d:%.2d:%.2d",
                       wday_name[timeptr->tm_wday],
                       mon_name[timeptr->tm_mon],
                       timeptr->tm_mday, timeptr->tm_hour,