Protect against ancient hwloc versions

Bring over the hwloc_bitmap_nexty_unset function and
use it only when linked against an ancient version
of hwloc

Signed-off-by: Ralph Castain <rhc@pmix.org>

src/hwloc/hwloc_base_util.c

@@ -1249,6 +1249,54 @@ void prte_hwloc_build_map(hwloc_topology_t topo,
     }
 }
 
+#if HWLOC_API_VERSION < 0x20000
+#define HWLOC_BITMAP_MAGIC 0x20091007
+#ifdef HWLOC_DEBUG
+#define HWLOC__BITMAP_CHECK(set) do {               \
+  assert((set)->magic == HWLOC_BITMAP_MAGIC);           \
+  assert((set)->ulongs_count >= 1);             \
+  assert((set)->ulongs_allocated >= (set)->ulongs_count);   \
+} while (0)
+#else
+#define HWLOC__BITMAP_CHECK(set)
+#endif
+#define HWLOC_SUBBITMAP_INDEX(cpu)      ((cpu)/(HWLOC_BITS_PER_LONG))
+#define HWLOC_SUBBITMAP_CPU_ULBIT(cpu)      ((cpu)%(HWLOC_BITS_PER_LONG))
+#define HWLOC_SUBBITMAP_ULBIT_TO(bit)       (HWLOC_SUBBITMAP_FULL>>(HWLOC_BITS_PER_LONG-1-(bit)))
+
+static int hwloc_bitmap_next_unset(const struct hwloc_bitmap_s * set, int prev_cpu)
+{
+    unsigned i = HWLOC_SUBBITMAP_INDEX(prev_cpu + 1);
+
+    HWLOC__BITMAP_CHECK(set);
+
+    if (i >= set->ulongs_count) {
+        if (!set->infinite)
+            return prev_cpu + 1;
+        else
+            return -1;
+    }
+
+    for(; i<set->ulongs_count; i++) {
+        /* subsets are unsigned longs, use ffsl */
+        unsigned long w = ~set->ulongs[i];
+
+        /* if the prev cpu is in the same word as the possible next one,
+           we need to mask out previous cpus */
+        if (prev_cpu >= 0 && HWLOC_SUBBITMAP_INDEX((unsigned) prev_cpu) == i)
+            w &= ~HWLOC_SUBBITMAP_ULBIT_TO(HWLOC_SUBBITMAP_CPU_ULBIT(prev_cpu));
+
+        if (w)
+            return hwloc_ffsl(w) - 1 + HWLOC_BITS_PER_LONG*i;
+    }
+
+    if (!set->infinite)
+        return set->ulongs_count * HWLOC_BITS_PER_LONG;
+
+    return -1;
+}
+#endif
+
 /* formatting core/hwt binding information as xml elements */
 int hwloc_bitmap_list_snprintf_exp(char *__hwloc_restrict buf, size_t buflen, 
                                    const struct hwloc_bitmap_s *__hwloc_restrict set,