Work around compile error in specific cases.

This appears to have been a bug in Haxe 4.0-4.1's HashLink target. `value++` failed, but `value = value + 1` was fine.

src/lime/system/ThreadPool.hx

@@ -425,7 +425,7 @@ class ThreadPool extends WorkOutput
 				{
 					while (!output.__jobComplete.value && (interruption = Thread.readMessage(false)) == null)
 					{
-						output.workIterations.value++;
+						output.workIterations.value = output.workIterations.value + 1;
 						event.job.doWork.dispatch(event.job.state, output);
 					}
 				}
@@ -521,7 +521,7 @@ class ThreadPool extends WorkOutput
 			{
 				do
 				{
-					workIterations.value++;
+					workIterations.value = workIterations.value + 1;
 					activeJob.doWork.dispatch(state, this);
 					timeElapsed = timestamp() - startTime;
 				}