New warning: `‘compiler_is_top_level_await’ defined but not used [-Wunused-function]`

# Bug report

### Bug description:

Popped up in https://github.com/python/cpython/pull/123546/files

I have a PR ready.

### CPython versions tested on:

CPython main branch

### Operating systems tested on:

Linux


### Linked PRs
* gh-123554
* gh-123578