virnuma: Implement virNumaGetDistances stub for non-NUMA

In case the libvirt is built without numactl support, we're
missing the virNumaGetDistances() stub so the linking fails:

  CCLD     libvirt_lxc
libvirt_lxc-nodeinfo.o: In function `virNodeCapsGetSiblingInfo':
/home/zippy/tmp/libvirt.git/src/nodeinfo.c:1763: undefined reference to `virNumaGetDistances'
collect2: error: ld returned 1 exit status
make[3]: *** [libvirt_lxc] Error 1

The issue was introduced in 77c830d8.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/util/virnuma.c

@@ -443,6 +443,17 @@ virNumaGetNodeCPUs(int node ATTRIBUTE_UNUSED,
                    _("NUMA isn't available on this host"));
     return -1;
 }
+
+int
+virNumaGetDistances(int node ATTRIBUTE_UNUSED,
+                    int **distances,
+                    int *ndistances)
+{
+    *distances = NULL;
+    *ndistances = 0;
+    VIR_DEBUG("NUMA isn't available on this host");
+    return 0;
+}
 #endif