Prefer 32-bit implementation for timing wheels on 32-bit systems.

This might make our timing-wheel code a tiny bit faster there.

Closes ticket 24688.

changes/bug24688

@@ -0,0 +1,3 @@
+  o Minor features (performance, 32-bit):
+    - Make our timing-wheel code run a tiny bit faster on 32-bit platforms,
+      by preferring 32-bit math to 64-bit. Closes ticket 24688.

src/common/timers.c

@@ -64,6 +64,11 @@ struct timeout_cb {
  * above TIMEOUT_MAX can also be super-inefficient. Choosing 5 here sets
  * timeout_max to 2^30 ticks, or 29 hours with our value for USEC_PER_TICK */
 #define WHEEL_NUM 5
+#if SIZEOF_VOID_P == 4
+/* On 32-bit platforms, we want to override wheel_bit, so that timeout.c will
+ * use 32-bit math. */
+#define WHEEL_BIT 5
+#endif
 #include "src/ext/timeouts/timeout.c"
 
 static struct timeouts *global_timeouts = NULL;