Auto-delete side-by-side "W...." folders other than our own if the target disk has less than 80% disk space left
If you're building lots of branches, you can run out of space due to multiple W.... folder variants sitting inside the build folder before the next scheduled clean-up happens.
If the target disk that the build folder resides on has less than 80% disk space left, we should delete all the W.... folders other than our own to clean up disk space. (Don't just clean up until we're under 80%, because that means we're likely to be hit when the build flips back to another branch, and we want to give ourselves the best opportunity to reuse intermediate files).