ARROW-9086 enabled Gandiva in our Homebrew formula, but when I tried to add that to the official Homebrew formula at release time, it failed. See some discussion at https://github.com/Homebrew/homebrew-core/pull/58581, though unfortunately the build logs are gone.
It turns out that the testing that Homebrew does is more thorough than the install/audit we do in CI. See https://github.com/Homebrew/homebrew-core/pull/58581/checks?check_run_id=915732878 for example. They install, build the bottle, then remove all dependencies and reinstall the bottle. Since this failed, what I think it means is that `llvm` is not a build-only dependency for Gandiva--it built but couldn't run successfully because `llvm` had been removed.