Avoid conflict with host definitions when cross-compiling

Certain platforms (e. g. BSD-based ones) define some ELF constants
according to host. This patch fixes problems with cross-building
Linux kernel on these platforms (e. g. building ARM 32-bit version
on x86-64 host).

Signed-off-by: Pavel Fedin <p.fedin@samsung.com>
Signed-off-by: Michal Marek <mmarek@suse.com>