Add swift_task_set_tsan_hooks()

This change will be sequenced:
  1. Call this hook from the TSan runtime
  2. Remove `dlsym()` lookup from Swift runtime

Author: Julian Lettner

stdlib/public/Concurrency/ThreadSanitizer.cpp

@@ -55,3 +55,9 @@ void swift::_swift_tsan_release(void *addr) {
     tsan_release(addr);
   }
 }
+
+SWIFT_EXPORT_FROM(swift_Concurrency) SWIFT_CC(c)
+void swift_task_set_tsan_hooks(TSanFunc *acquire, TSanFunc *release) {
+  tsan_acquire = acquire;
+  tsan_release = release;
+}