intrusive_array: prepare for std::strong_ordering

Newer comparators can return std::strong_ordering, so don't
expect an int.

utils/intrusive-array.hh

@@ -271,7 +271,7 @@ public:
         int i = 0;
 
         do {
-            int x = cmp(_data[i].object, val);
+            auto x = cmp(_data[i].object, val);
             if (x >= 0) {
                 match = (x == 0);
                 break;