tools/virtio: fix build break for aarch64

"-mfunction-return=thunk -mindirect-branch-register" are only valid
for x86. So introduce compiler operation check to avoid such issues

Fixes: 0d0ed400 ("tools/virtio: enable to build with retpoline")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Message-Id: <20230323040024.3809108-1-peng.fan@oss.nxp.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>