mini-os: Fix build error when !HAVE_LIBC
mini-os: Fix build error when !HAVE_LIBC

Signed-off-by: Yu Zhiguo <8054a20a08d4403eea8d396e877a5f535cd398d4@cn.fujitsu.com>

rowhit/xen-minios,rowhit/xen-minios,rowhit/xen-minios