[Concurrency] Traffic in underlying C type rather than JobFlags.

Suppresses a warning about returning a C++ type from a C entrypoint,
fixing rdar://71731181.

Author: DougGregor

include/swift/Runtime/Concurrency.h

@@ -175,8 +175,7 @@ bool swift_task_removeStatusRecord(AsyncTask *task,
                                    TaskStatusRecord *record);
 
 SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(swift)
-JobFlags
-swift_task_getJobFlags(AsyncTask* task);
+size_t swift_task_getJobFlags(AsyncTask* task);
 
 /// This should have the same representation as an enum like this:
 ///    enum NearestTaskDeadline {

stdlib/public/Concurrency/Task.cpp

@@ -352,6 +352,6 @@ void swift::swift_task_run(AsyncTask *taskToRun) {
   taskToRun->run(ExecutorRef::generic());
 }
 
-JobFlags swift::swift_task_getJobFlags(AsyncTask *task) {
-  return task->Flags;
+size_t swift::swift_task_getJobFlags(AsyncTask *task) {
+  return task->Flags.getOpaqueValue();
 }