[release/homebrew] Always use x64 binaries on macOS
[release/homebrew] Always use x64 binaries on macOS

We no longer support ia32 Macs (see linked issue).

Bug: https://github.com/dart-lang/sdk/issues/39810
Change-Id: I5fc6ab6a9074e54a90e8480d0ede416a237733cf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/130360
Reviewed-by: William Hesse <a821cddceae7dc400f272e3cb1a72f400f9fed6d@google.com>

dart-lang/homebrew-dart,dart-lang/homebrew-dart,dart-lang/homebrew-dart