Reduces the time for a build after touching `CodegenRust.py` by 58s for me.
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix#12529 (github issue number if applicable).
- [X] These changes do not require tests because it's a build performance optimization
Source-Repo: https://github.com/servo/servo
Source-Revision: cdf225c26e04ac8a2f3294ab32999ec482db8cd4
Ready for review.
Final link step on android fails, but we know how to fix it and will add it to this branch soon.
Source-Repo: https://github.com/servo/servo
Source-Revision: 2cc08f289ab909de44fa09a07b2c43b70ce379b9
