tests/timer: Skip test_timeval_to_iso8601_overflow if we can't overflow a GTimeVal

On 32 bit systems, the size of a long might be the same as the size of
an int. In that case, we won't be able to get an overflow when
converting from a GTimeVal to a time_t. Skip the test for this in that
case.

Closes #1509


(cherry picked from commit f697f6aa08)

glib/tests/timer.c

@@ -258,6 +258,12 @@ test_timeval_to_iso8601_overflow (void)
   GTimeVal val;
   gchar *out = NULL;
 
+  if ((glong) G_MAXINT == G_MAXLONG)
+    {
+      g_test_skip ("G_MAXINT == G_MAXLONG - we can't make g_time_val_to_iso8601() overflow.");
+      return;
+    }
+
   g_unsetenv ("TZ");
 
   val.tv_sec = G_MAXLONG;