Track the 'awaiter return' call stack use it to detect uncaught exceptions in async functions

runtime/vm/exceptions.h

Index: runtime/vm/exceptions.h
diff --git a/runtime/vm/exceptions.h b/runtime/vm/exceptions.h
index df4c44c4bd157f16374cdd7588f8862c3ef5aab3..3f61a35e918fc16f4d3ffc301bac11886264ff71 100644
--- a/runtime/vm/exceptions.h
+++ b/runtime/vm/exceptions.h
@@ -97,6 +97,7 @@ struct ExceptionHandlerInfo {
   int16_t outer_try_index;     // Try block index of enclosing try block.
   int8_t needs_stacktrace;     // True if a stacktrace is needed.
   int8_t has_catch_all;        // Catches all exceptions.
+  int8_t is_generated;         // True if this is a generated handler.
 };
 
 }  // namespace dart