FreeBSD: Fixes required to build ZFS on PowerPC

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #10622

module/zfs/vdev_raidz_math.c

@@ -65,7 +65,7 @@ const raidz_impl_ops_t *raidz_all_maths[] = {
 	&vdev_raidz_aarch64_neon_impl,
 	&vdev_raidz_aarch64_neonx2_impl,
 #endif
-#if defined(__powerpc__)
+#if defined(__powerpc__) && defined(__altivec__)
 	&vdev_raidz_powerpc_altivec_impl,
 #endif
 };