Description of the feature request:

Per #16937, while the XDG Base Directory spec is more commonly adopted on Linux, there's little I'm aware of in the way of supporting it on macOS for those users who set the environment variables. Is this something that can be added as a secondary option for that platform, or is there something special about /private/var/tmp as an output root?

Which category does this issue belong to?

Core

What underlying problem are you trying to solve with this feature?

A similar issue as interrogated with #16937, but for macOS instead of just Linux.

Which operating system are you running Bazel on?

macOS 15.3

What is the output of bazel info release?

release 8.0.1