New try to fix test_time.test_AsSecondsDouble() on x86 buildbots.

Use volatile keyword in _PyTime_AsSecondsDouble()

Python/pytime.c

@@ -332,16 +332,21 @@ _PyTime_FromMillisecondsObject(_PyTime_t *t, PyObject *obj, _PyTime_round_t roun
 double
 _PyTime_AsSecondsDouble(_PyTime_t t)
 {
+    /* volatile avoids optimization changing how numbers are rounded */
+    volatile double d;
+
     if (t % SEC_TO_NS == 0) {
         _PyTime_t secs;
         /* Divide using integers to avoid rounding issues on the integer part.
            1e-9 cannot be stored exactly in IEEE 64-bit. */
         secs = t / SEC_TO_NS;
-        return (double)secs;
+        d = (double)secs;
     }
     else {
-        return (double)t / 1e9;
+        d = (double)t;
+        d /= 1e9;
     }
+    return d;
 }
 
 PyObject *