Fix bug in Dispatch executor preventing long sleeps
Dispatch executor's swift_task_enqueueGlobalWithDelayImpl adds the
requested delay to the current time and enqueues the job to run at that
time. This has a bug when using a very large delay on the order of 2^63
to 2^64 nanoseconds because dispatch_time(), which is used to preform
the now + delay calculation, returns DISPATCH_TIME_FOREVER. However,
dispatch_after(), which is used to actually enqueue the job, has
undefined behavior for this time; the result in practice is that the job
is immediately run.
This change resolves the bug by leaking the job if the result of
dispatch_time is DISPATCH_TIME_FOREVER. This should effectively be the
same as the job getting delayed forever.
Radar-Id: rdar://problem/89455918
