powerpc64 musl

[mcandre]

Checklist

• [x] I've looked through the issues and pull requests for similar request
• [ ] This feature could be solved with a custom image (optional)

Describe your request

Rust 1.85 promotes a new tier 2 platform, PowerPC 64 musl:

https://github.com/rust-lang/rust/releases/tag/1.85.0

Describe why this would be a good inclusion for cross

Presumably, Alpine, Void, or other musl/Linux OS's offer ppc64 editions which would benefit from ppc64 musl Rust binaries.