add x86_64 > x64 mapping for darwin

[jhheider]

Issue # (if available)

(skipped issue; will open if desired.)

Description of changes

add Makefile target to redirect llrt-darwin-x86_64.zip to llrt-darwin-x64.zip, mirroring the same logic used for linux. It's a one-line Makefile change, so it shouldn't impact any of the code.

Checklist

• [ ] Created unit tests in tests/unit and/or in Rust for my feature if needed
• [ ] Ran make fix to format JS and apply Clippy auto fixes
• [ ] Made sure my code didn't add any additional warnings: make check
• [ ] Updated documentation if needed (API.md/README.md/Other)

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[richarddavison]

Thank you! Nice catch!

[jhheider]

Happy to help!