LINUX: CURRENT_TIME macro goes away.

LINUX: CURRENT_TIME macro goes away.

Check if the macro exists, define it if it does not.

Reviewed-on: https://gerrit.openafs.org/12611
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit b47dc5482da614742b01dcc62d5e11d766a9432f)

Change-Id: I1ed3706e830b98436a5a22d99fa338b01fd5b997
Reviewed-on: https://gerrit.openafs.org/12624
Tested-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>