Default to using /tmp for temporary directory base if both XDG_CACHE_HOME and...

Default to using /tmp for temporary directory base if both XDG_CACHE_HOME and TMPDIR are not defined in the environment.

Without this patch the script would end up trying to create temporary directories in the root and fail.
2 jobs for !41 with temp_directory_fallback in 2 minutes and 46 seconds (queued for 1 second)
merge request