Instead, use the `%target-swift-5.1-abi-triple` substitution to compile the tests
for deployment to the minimum OS versions required for use of _Concurrency APIs.
This is done using a condition variable upon which the awaiting thread
will block if the continuation has not be resumed by the point of await.
The resuming thread will signal this condition variable, thereby
unblocking the awaiting thread.
Rdar://99977665
