Installing axoupdater from source has broken

[mistydemeo]

By default, we try to fetch prebuilt axoupdater binaries. If that fails, we fall back to building from source; this happens most often when the requested target triple is an architecture we don't (yet) package axoupdater for. This appears to have broken at some point - we're seeing that the build completes, but copying the built file to its target fails, at least for aarch64-pc-windows.

  × failed to copy asset from /tmp/t18f6-0/bin/axoupdater.exe to /__w/cargodisttest/cargodisttest/target/distrib/
  │ axolotlsay-aarch64-pc-windows-msvc-update
  ╰─▶ No such file or directory (os error 2)

https://github.com/mistydemeo/cargodisttest/actions/runs/11827127509/job/32954740155#logs

[mistydemeo]

It turns out this is specific to cross-compilation in #1529. Since we're building with cargo, we need to make sure that all of the rest of the cross-compilation machinery gets activated here too.