1, do not hardcode libnl's cflags
    when cross compile CRIU, libnl's header file should not point to host.

2, remove link to rt
    Android NDK doesn't have library rt, and CRIU is not really need it,
    so disable it to pass link

Cc: Chen Hu <hu1.chen@intel.com>
Signed-off-by: Zhang Ning <ning.a.zhang@intel.com>
Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com>