host-utils: Move 128-bit guard macro to .c file

It is not possible to implement functions in host-utils.c for
architectures with quadwords because the guard is implemented in the
Makefile. This patch move the guard out of the Makefile to the
implementation file.

Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
