- Add some functions to ASYNCIFY_ADD
A function that calls an asynchronous function via a function pointer
must be added to ASYNCIFY_ADD, even if it had a direct call to
another asynchronous function, so that the indirect call itself is
instrumented.
- Add dummy emscripten_sleep() call to send_agsevent
Because adding a function to ASYNCIFY_ADD does not make its callers
instrumented transitively.