Fix compiler error with -fno-exceptions.

Change-Id: I617d7fe81769f16097b911b341086b4aee8b5110
diff --git a/platform/api/task_runner.h b/platform/api/task_runner.h
index c061086..948eb08 100644
--- a/platform/api/task_runner.h
+++ b/platform/api/task_runner.h
@@ -22,7 +22,13 @@
 //     B runs (even if A and B run on different threads).
 class TaskRunner {
  public:
+// Seem to get an error using clang when compiling with -fno-exceptions:
+//   error: implicit instantiation of undefined template 'std::__1::packaged_task<void () noexcept>'
+#if __has_feature(cxx_exceptions)
   using Task = std::packaged_task<void() noexcept>;
+#else
+  using Task = std::packaged_task<void()>;
+#endif
 
   virtual ~TaskRunner() = default;