AAL: new StrictProvenance feature flag

src/aal/aal.h

@@ -36,6 +36,12 @@ namespace snmalloc
      * This architecture cannot access cpu cycles counters.
      */
     NoCpuCycleCounters = (1 << 1),
+    /**
+     * This architecture enforces strict pointer provenance; we bound the
+     * pointers given out on malloc() and friends and must, therefore retain
+     * internal high-privilege pointers for recycling memory on free().
+     */
+    StrictProvenance = (1 << 2),
   };
 
   /**