Forward CMAKE_TOOLCHAIN_FILE to arrow build for sdk cross-compilation

[SunDoge]

What

Add -DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE} to the cmake file to fix #7445

Checklist

• I have read and agree to Contributor Guide and the Code of Conduct
• I've included a screenshot or gif (if applicable)
• I have tested the web demo (if applicable):
  • Using examples from latest main build: rerun.io/viewer
  • Using full set of examples from nightly build: rerun.io/viewer
• The PR title and labels are set such as to maximize their usefulness for the next release's CHANGELOG
• If applicable, add a new check to the release checklist!
• If have noted any breaking changes to the log API in CHANGELOG.md and the migration guide

• PR Build Summary
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[Wumpf]

thanks!

[emilk]

Will this close

• Rerun C++ SDK: undefined symbols (arch mismatch) when cross-compiling for macOS x64 #7248

?

[SunDoge]

Will this close

* [Rerun C++ SDK: undefined symbols (arch mismatch) when cross-compiling for macOS x64 #7248](https://github.com/rerun-io/rerun/issues/7248)

?

Unfortunately no. I've tested on my macbook pro.