gdate: Call tzset before localtime_r

From `man 3 ctime`:
  According to POSIX.1, localtime() is required to behave as though tzset(3)
  was called, while localtime_r() does not have this requirement.
  For portable code, tzset(3) should be called before localtime_r().

glib/gdate.c

@@ -1392,6 +1392,7 @@ _g_localtime (time_t timet, struct tm *out_tm)
   gboolean success = TRUE;
 
 #ifdef HAVE_LOCALTIME_R
+  tzset ();
   if (!localtime_r (&timet, out_tm))
     success = FALSE;
 #else