LU-2675 build: assume __linux__ and __KERNEL__

Assume that __linux__is defined everywhere and that __KERNEL__ is
defined in most of lustre/.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ia04e7ed4c3ab3e8ca205e14eaa1824536aedd1e3
Reviewed-on: http://review.whamcloud.com/11437


Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Jenkins
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Oleg Drokin <oleg.drokin@intel.com>