Added unit test Async/GetFunctorStartAdress which just calls…

Added unit test Async/GetFunctorStartAdress which just calls GetFunctorStartAdress() to provoke a core dump when running on ARM platforms. If you want to reproduce it, you don't need real ARM hardware. Just build Cap'n'proto with an ARM compiler and run it via QEMU.

c++/src/kj/async-test.c++

@@ -26,6 +26,10 @@
 namespace kj {
 namespace {
 
+TEST(Async, GetFunctorStartAddress) {
+  EXPECT_TRUE(nullptr != _::GetFunctorStartAddress<>::apply([](){return 0;}));
+}
+
 TEST(Async, EvalVoid) {
   EventLoop loop;
   WaitScope waitScope(loop);