`EXCEPTION_CATCHING_ALLOWED=xxx` can have smaller code size than `EXCEPTION_CATCHING_ALLOWED=`

For some reason we have a test that tries to verify that the empty allow list produces smaller code than the non-empty one, even when the list contains functions that don't exist.

See `other.test_exceptions_allowed`.

I recently made a change that somehow means that `-O3`, `-Oz` and `-Os` now give very slightly better results when specifying ``EXCEPTION_CATCHING_ALLOWED=fake` then when specifying the empty list. I have no idea who/why this could be. Its not clear that fixing it is particularly important either since we are moving away from emscripten exceptions.