make: combine arch-specific options together

DEFINES, LDARCH, VDSO in one place - visually simpler, more terse.

Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>