LU-3441 build: Allow for native KNC compilation

LU-3441 build: Allow for native KNC compilation

The cross-compilation support (LU-2752) assumes that K1OM will
only be built in a cross-compile environment. To allow for
native compilation we only perform the cross compilation check
if $cross_compile is defined to yes.

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: I93fd9c2f7d29dd9567cfcd93013df09271d65dc2
Reviewed-on: http://review.whamcloud.com/6558
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Minh Diep <minh.diep@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>