Fixes a bug whereby derivations importing (gnu build linux-container),
such as the 'bitlbee' and 'tor' services, would depend on the
user's (guix config) file, which was pulled as a dependency of (guix
utils). As a result, those derivations would vary from user to user.
* gnu/build/linux-container.scm (call-with-temporary-directory): New
procedure.