criu: wrap compatible code with CONFIG_COMPAT

As we will not support *native* 32-bit i386 build, I dropped some
ifdefs, introducing instead of ifdef(CONFIG_X86_64) --
ifdef(CONFIG_COMPAT).

CRIU should build now without ia32 Glibc and gcc-multilib support.
Maybe I should add some warning that the build is made without
compatible task support (or criu check should print that),
will do as compat patches hit master.

Fixes: #181

Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>