Auto merge of #22000 - oli-obk:master, r=jdm

Add a workaround for a rustc ICE

While https://github.com/rust-lang/rust/issues/55223 is being fixed, this workaround will allow servo to compile on the latest nightly rustc

r? @SimonSapin

---

- [ ] `./mach build -d` does not report any errors
  * I'm getting
  ```
    Collecting voluptuous==0.10.5 (from -r /home/oliver/Projects/rust/servo/python/requirements.txt (line 18))
      Using cached https://files.pythonhosted.org/packages/c3/81/c84f8a3e723b760fdd1c41fc80201cb80cd29c1bce5159d8918c58df7d2a/voluptuous-0.10.5.tar.gz
        Complete output from command python setup.py egg_info:
        Traceback (most recent call last):
          File "<string>", line 1, in <module>
          File "/tmp/pip-install-Qdty2x/voluptuous/setup.py", line 16, in <module>
            f.write(long_description)
        UnicodeEncodeError: 'ascii' codec can't encode character u'\u2019' in position 1229: ordinal not in range(128)
    ```
    locally, no clue how to continue from there. The script crate compiles fine with `cargo build`
- [ ] `./mach test-tidy` does not report any errors

- [X] These changes do not require tests because the `script` crate just won't compile without this change

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