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 77991533a4c3cec7929c40f3db40170b915dd08f..c2a3350042b24ec8941869ff52528da1d6f4e385 100644
--- a/runtime/vm/exceptions.h
+++ b/runtime/vm/exceptions.h
@@ -99,6 +99,7 @@ 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