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- [x] Add new / update outdated documentation

<div align="center">
  <a href="https://github.com/pyodide/pyodide">
  <img src="./docs/_static/img/pyodide-logo-readme.png" alt="Pyodide">
  </a>
</div>

[![NPM Latest Release](https://img.shields.io/npm/v/pyodide)](https://www.npmjs.com/package/pyodide)
[![PyPI Latest Release](https://img.shields.io/pypi/v/pyodide-build.svg)](https://pypi.org/project/pyodide-build/)
[![Build Status](https://circleci.com/gh/pyodide/pyodide.png)](https://circleci.com/gh/pyodide/pyodide)
[![Documentation Status](https://readthedocs.org/projects/pyodide/badge/?version=stable)](https://pyodide.readthedocs.io/?badge=stable)

Pyodide is a Python distribution for the browser and Node.js based on WebAssembly.

## What is Pyodide?

Pyodide is a port of CPython to WebAssembly/[Emscripten](https://emscripten.org/).

Pyodide makes it possible to install and run Python packages in the browser with
[micropip](https://pyodide.org/en/stable/usage/api/micropip-api.html). Any pure
Python package with a wheel available on PyPi is supported. Many packages with C
extensions have also been ported for use with Pyodide. These include many
general-purpose packages such as regex, PyYAML, lxml and scientific Python
packages including NumPy, pandas, SciPy, Matplotlib, and scikit-learn.

Pyodide comes with a robust Javascript ⟺ Python foreign function interface so
that you can freely mix these two languages in your code with minimal
friction. This includes full support for error handling (throw an error in one
language, catch it in the other), async/await, and much more.

When used inside a browser, Python has full access to the Web APIs.

## Try Pyodide (no installation needed)

Try Pyodide in a
[REPL](https://pyodide.org/en/stable/console.html) directly in
your browser. For further information, see the
[documentation](https://pyodide.org/en/stable/).

## Getting Started

Pyodide offers three different ways to get started depending on your needs and
technical resources. These include:

- Use a hosted distribution of Pyodide: see the [Getting
  Started](https://pyodide.org/en/stable/usage/quickstart.html) documentation.
- Download a version of Pyodide from the [releases
  page](https://github.com/pyodide/pyodide/releases/) and serve it
  with a web server.
- [Build Pyodide from source](https://pyodide.org/en/stable/development/building-from-sources.html)
  - Build natively with `make`: primarily for Linux users who want to
    experiment or contribute back to the project.
  - [Use a Docker image](https://pyodide.org/en/stable/development/building-from-sources.html#using-docker):
    recommended for Windows and macOS users and for Linux users who prefer a
    Debian-based Docker image with the dependencies already installed.

## History

Pyodide was created in 2018 by [Michael Droettboom](https://github.com/mdboom)
at Mozilla as part of the [Iodide
project](https://github.com/iodide-project/iodide). Iodide is an experimental
web-based notebook environment for literate scientific computing and
communication.

Iodide is no longer maintained. If you want to use Pyodide in an interactive
client-side notebook, see [Pyodide notebook
environments](https://pyodide.org/en/stable/project/related-projects.html#notebook-environments-ides-repls).

## Contributing

Please view the [contributing
guide](https://pyodide.org/en/stable/development/contributing.html) for tips
on filing issues, making changes, and submitting pull requests. Pyodide is an
independent and community-driven open-source project. The decision-making
process is outlined in the [Project
governance](https://pyodide.org/en/stable/project/governance.html).

## Communication

- Blog: [blog.pyodide.org](https://blog.pyodide.org/)
- Mailing list: [mail.python.org/mailman3/lists/pyodide.python.org/](https://mail.python.org/mailman3/lists/pyodide.python.org/)
- Gitter: [gitter.im/pyodide/community](https://gitter.im/pyodide/community)
- Twitter: [twitter.com/pyodide](https://twitter.com/pyodide)
- Stack Overflow: [stackoverflow.com/questions/tagged/pyodide](https://stackoverflow.com/questions/tagged/pyodide)

## License

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

<div align="center">
  <a href="https://github.com/pyodide/pyodide">
  <img src="./docs/_static/img/pyodide-logo-readme.png" alt="Pyodide">
  </a>
</div>

[![NPM Latest Release](https://img.shields.io/npm/v/pyodide)](https://www.npmjs.com/package/pyodide)
[![PyPI Latest Release](https://img.shields.io/pypi/v/pyodide-build.svg)](https://pypi.org/project/pyodide-build/)
[![Build Status](https://circleci.com/gh/pyodide/pyodide.png)](https://circleci.com/gh/pyodide/pyodide)
[![Documentation Status](https://readthedocs.org/projects/pyodide/badge/?version=stable)](https://pyodide.readthedocs.io/?badge=stable)

Pyodide is a Python distribution for the browser and Node.js based on WebAssembly.

## What is Pyodide?

Pyodide is a port of CPython to WebAssembly/[Emscripten](https://emscripten.org/).

Pyodide makes it possible to install and run Python packages in the browser with
[micropip](https://pyodide.org/en/stable/usage/api/micropip-api.html). Any pure
Python package with a wheel available on PyPi is supported. Many packages with C
extensions have also been ported for use with Pyodide. These include many
general-purpose packages such as regex, PyYAML, lxml and scientific Python
packages including NumPy, pandas, SciPy, Matplotlib, and scikit-learn.

Pyodide comes with a robust Javascript ⟺ Python foreign function interface so
that you can freely mix these two languages in your code with minimal
friction. This includes full support for error handling (throw an error in one
language, catch it in the other), async/await, and much more.

When used inside a browser, Python has full access to the Web APIs.

## Try Pyodide (no installation needed)

Try Pyodide in a
[REPL](https://pyodide.org/en/stable/console.html) directly in
your browser. For further information, see the
[documentation](https://pyodide.org/en/stable/).

## Getting Started

Pyodide offers three different ways to get started depending on your needs and
technical resources. These include:

- Use a hosted distribution of Pyodide: see the [Getting
  Started](https://pyodide.org/en/stable/usage/quickstart.html) documentation.
- Download a version of Pyodide from the [releases
  page](https://github.com/pyodide/pyodide/releases/) and serve it
  with a web server.
- [Build Pyodide from source](https://pyodide.org/en/stable/development/building-from-sources.html)
  - Build natively with `make`: primarily for Linux users who want to
    experiment or contribute back to the project.
  - [Use a Docker image](https://pyodide.org/en/stable/development/building-from-sources.html#using-docker):
    recommended for Windows and macOS users and for Linux users who prefer a
    Debian-based Docker image with the dependencies already installed.

## History

Pyodide was created in 2018 by [Michael Droettboom](https://github.com/mdboom)
at Mozilla as part of the [Iodide
project](https://github.com/iodide-project/iodide). Iodide is an experimental
web-based notebook environment for literate scientific computing and
communication.

Iodide is no longer maintained. If you want to use Pyodide in an interactive
client-side notebook, see [Pyodide notebook
environments](https://pyodide.org/en/stable/project/related-projects.html#notebook-environments-ides-repls).

## Contributing

Please view the [contributing
guide](https://pyodide.org/en/stable/development/contributing.html) for tips
on filing issues, making changes, and submitting pull requests. Pyodide is an
independent and community-driven open-source project. The decision-making
process is outlined in the [Project
governance](https://pyodide.org/en/stable/project/governance.html).

## Communication

- Blog: [blog.pyodide.org](https://blog.pyodide.org/)
- Mailing list: [mail.python.org/mailman3/lists/pyodide.python.org/](https://mail.python.org/mailman3/lists/pyodide.python.org/)
- Gitter: [gitter.im/pyodide/community](https://gitter.im/pyodide/community)
- Twitter: [twitter.com/pyodide](https://twitter.com/pyodide)
- Stack Overflow: [stackoverflow.com/questions/tagged/pyodide](https://stackoverflow.com/questions/tagged/pyodide)

## License

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