www-client/firefox: support aarch64-unknown-linux-musl

[mojyack]

Workaround for rust-bin broke firefox built for arm64.
This PR or #35268 will fix this.

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[gentoo-bot]

Pull Request assignment

Submitter: @mojyack
Areas affected: ebuilds
Packages affected: www-client/firefox

www-client/firefox: @gentoo/mozilla

Linked bugs

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[gentoo-repo-qa-bot]

Pull request CI report

Report generated at: 2024-05-12 05:44 UTC
Newest commit scanned: 7c29140
Status: ✅ good

There are existing issues already. Please look into the report to make sure none of them affect the packages in question:
https://qa-reports.gentoo.org/output/gentoo-ci/cb463cf3f1/output.html