Same as T391426: Work around glibc timer aliasing in Excimer but in LuaSandbox. We don't want LuaSandbox either generating orphaned in-flight timer events, or receiving and acting on them in its timeout handler.

The code is so similar to Excimer that I'm investigating having a timer library shared between them. Then LuaSandbox will get timer functionality on Mac OS as a bonus, using @mszabo's work on the kqueue implementation in Excimer.