[macOS] Only bundle gen_snapshot_${target_arch}

[cbracken]

On most platforms, we support only a single host architecture and a single target architecture per build. macOS supports both arm64 and x86_64 host platforms via multi-arch (universal) binaries generated with the lipo tool and as such, we have two gen_snapshot binaries, one for each target architecture. These binaries are universal binaries named gen_snapshot_${target_arch}. The unqualified gen_snapshot binary used for other platforms is unused on macOS.

This eliminates the unqualified binary from the uploaded bundles used by the tool.

Cleanup related to: Issue: https://github.com/flutter/flutter/issues/101138 Issue: https://github.com/flutter/flutter/issues/69157

Pre-launch Checklist

• [X] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [X] I read the Tree Hygiene wiki page, which explains my responsibilities.
• [X] I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• [X] I listed at least one issue that this PR fixes in the description above.
• [ ] I added new tests to check the change I am making or feature I am adding, or the PR is test-exempt. See testing the engine for instructions on writing and running engine tests.
• [X] I updated/added relevant documentation (doc comments with ///).
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• [X] All existing and new tests are passing.

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[flutter-dashboard[bot]]

This pull request executed golden file tests, but it has not been updated in a while (20+ days). Test results from Gold expire after as many days, so this pull request will need to be updated with a fresh commit in order to get results from Gold.

[flutter-dashboard[bot]]

This pull request has been changed to a draft. The currently pending flutter-gold status will not be able to resolve until a new commit is pushed or the change is marked ready for review again.

[Piinks]

(PR triage): @cbracken is this still on your radar?

[cbracken]

I'll file a proper issue for this, self-assign and then close this once I've collected up the error messages. Thanks for the reminder.

[jmagman]

I'll file a proper issue for this, self-assign and then close this once I've collected up the error messages. Thanks for the reminder.

@cbracken were you able to file the issue? Ideally we should close all engine PRs.

[cbracken]

Issue filed at https://github.com/flutter/flutter/issues/161245