Export PATH and ERRNO_CODES from Emscripten. ### Description

Fixes #2577 by exporting `PATH` and `ERRNO_CODES` from Emscripten

### Checklists

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

# pyodide-build

Tools for building Pyodide.

See [http://github.com/pyodide/pyodide](http://github.com/pyodide/pyodide) for
more information.

## License

Pyodide uses the [Mozilla Public License Version
2.0](https://choosealicense.com/licenses/mpl-2.0/).

# pyodide-build

Tools for building Pyodide.

See [http://github.com/pyodide/pyodide](http://github.com/pyodide/pyodide) for
more information.

## License

Pyodide uses the [Mozilla Public License Version
2.0](https://choosealicense.com/licenses/mpl-2.0/).
