kvm tools: Get correct 64-bit types on PPC64 and link appropriately

kvmtool's types.h includes <asm/types.h>, which by default on PPC64 brings in
int-l64.h; define __SANE_USERSPACE_TYPES__ to get LL64 types.

This patch also adds CFLAGS to the final link, so that any -m64 is obeyed
when linking, too.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>