[Threading][UnitTests] Don't use threads in the unit test in no-threads mode.

If the threading package is set to "none", don't actually use threads in the
unit tests.

rdar://95011060

Author: al45tair

unittests/Threading/ThreadingHelpers.h

@@ -15,6 +15,32 @@
 
 #include <thread>
 
+#if SWIFT_THREADING_NONE
+
+template <typename ThreadBody, typename AfterSpinRelease>
+void threadedExecute(int threadCount, ThreadBody threadBody,
+                     AfterSpinRelease afterSpinRelease) {
+  for (int i = 0; i < threadCount; ++i) {
+    threadBody(i);
+  }
+}
+
+template <typename M, typename C, typename ConsumerBody, typename ProducerBody>
+void threadedExecute(M &mutex, C &condition, bool &doneCondition,
+                     ConsumerBody consumerBody, ProducerBody producerBody) {
+  for (int i = 1; i <= 5; ++i) {
+    producerBody(i);
+  }
+  mutex.withLockThenNotifyAll(condition, [&] {
+    doneCondition = true;
+  });
+  for (int i = 1; i <= 8; ++i) {
+    consumerBody(i);
+  }
+}
+
+#else // !SWIFT_THREADING_NONE
+
 // When true many of the threaded tests log activity to help triage issues.
 static bool trace = false;
 
@@ -131,4 +157,6 @@ void threadedExecute(M &mutex, C &condition, bool &doneCondition,
   }
 }
 
+#endif // !SWIFT_THREADING_NONE
+
 #endif