❯ ./mach build
Traceback (most recent call last):
  File "/home/jschwender/Dev/servo/./mach", line 45, in <module>
    main(sys.argv)
    ~~~~^^^^^^^^^^
  File "/home/jschwender/Dev/servo/./mach", line 24, in main
    mach = mach_bootstrap.bootstrap(topdir)
  File "/home/jschwender/Dev/servo/python/mach_bootstrap.py", line 251, in bootstrap
    mach.load_commands_from_file(os.path.join(topdir, path), module_name)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jschwender/Dev/servo/python/mach/mach/main.py", line 260, in load_commands_from_file
    spec.loader.exec_module(module)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^
  File "<frozen importlib._bootstrap_external>", line 1022, in exec_module
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "/home/jschwender/Dev/servo/python/servo/testing_commands.py", line 24, in <module>
    import wpt.run
  File "/home/jschwender/Dev/servo/python/wpt/run.py", line 27, in <module>
    from wptrunner import wptrunner
  File "/home/jschwender/Dev/servo/tests/wpt/tests/tools/wptrunner/wptrunner/wptrunner.py", line 11, in <module>
    import wptserve
  File "/home/jschwender/Dev/servo/tests/wpt/tests/tools/wptserve/wptserve/__init__.py", line 1, in <module>
    from .server import WebTestHttpd, WebTestServer, Router  # noqa: F401
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/jschwender/Dev/servo/tests/wpt/tests/tools/wptserve/wptserve/server.py", line 29, in <module>
    from . import routes as default_routes
  File "/home/jschwender/Dev/servo/tests/wpt/tests/tools/wptserve/wptserve/routes.py", line 1, in <module>
    from . import handlers
  File "/home/jschwender/Dev/servo/tests/wpt/tests/tools/wptserve/wptserve/handlers.py", line 13, in <module>
    from .request import Authentication
  File "/home/jschwender/Dev/servo/tests/wpt/tests/tools/wptserve/wptserve/request.py", line 4, in <module>
    import cgi
ModuleNotFoundError: No module named 'cgi'