__set_stack_limits not found in SIDE_MODULE=2

`__set_stack_limits` gets optimized away when I build a side module via `-s SIDE_MODULE=2 -s ASSERTIONS=2`.
Then when I try to load this side module into the main module (built with `-s MAIN_MODULE=2 -s ASSERTIONS=2`), I get an error:

```
TypeError: moduleExports.__set_stack_limits is not a function
```
due to the STACK_OVERFLOW_CHECK when `ASSERTIONS=2`.

It doesn't seem to work even after adding `-s EXPORTED_FUNCTIONS=['__set_stack_limits']`