timing wheels should use 32-bit math on 32-bit platforms

I think this might help our 32-bit performance a bit.

Not putting this in needs_review yet, since it needs more analysis.

diff --git a/src/common/timers.c b/src/common/timers.c
index 93cde7de5fbd4b..3c806b7f4b422a 100644
--- a/src/common/timers.c
+++ b/src/common/timers.c
@@ -66,6 +66,11 @@ struct timeout_cb {
  * above TIMEOUT_MAX can also be super-inefficent. 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;