core: better handle empty topology errors

Don't abort if the topology is empty, just return an error.
Also return an error if there are no PU or no NUMA node
(empty means there are no PU AND no NUMA node).

Always print a error message on stderr since this shouldn't
happen in normal cases.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>

hwloc/topology.c

@@ -3133,11 +3133,19 @@ hwloc_discover(struct hwloc_topology *topology)
   hwloc_filter_bridges(topology, topology->levels[0][0]);
   hwloc_debug_print_objects(0, topology->levels[0][0]);
 
-  hwloc_debug("%s", "\nRemoving empty objects except numa nodes and PCI devices\n");
+  hwloc_debug("%s", "\nRemoving empty objects\n");
   remove_empty(topology, &topology->levels[0][0]);
-    if (!topology->levels[0][0]) {
+  if (!topology->levels[0][0]) {
     fprintf(stderr, "Topology became empty, aborting!\n");
-    abort();
+    return -1;
+  }
+  if (hwloc_bitmap_iszero(topology->levels[0][0]->cpuset)) {
+    fprintf(stderr, "Topology does not contain any PU, aborting!\n");
+    return -1;
+  }
+  if (hwloc_bitmap_iszero(topology->levels[0][0]->nodeset)) {
+    fprintf(stderr, "Topology does not contain any NUMA node, aborting!\n");
+    return -1;
   }
   hwloc_debug_print_objects(0, topology->levels[0][0]);