Fix tag collision between ENABLE_DISCLAIM and KEEP_BACK_PTRS

* fnlz_mlc.c (FINALIZER_CLOSURE_FLAG): New macro (defined to 0x2 in
case KEEP_BACK_PTRS or MAKE_BACK_GRAPH, otherwise to 0x1).
* fnlz_mlc.c (GC_finalized_disclaim, GC_finalized_malloc): Use
FINALIZER_CLOSURE_FLAG instead of 0x1.

fnlz_mlc.c

@@ -21,11 +21,18 @@
 
 STATIC int GC_finalized_kind = 0;
 
+#if defined(KEEP_BACK_PTRS) || defined(MAKE_BACK_GRAPH)
+  /* The first bit is already used for a debug purpose. */
+# define FINALIZER_CLOSURE_FLAG 0x2
+#else
+# define FINALIZER_CLOSURE_FLAG 0x1
+#endif
+
 STATIC int GC_CALLBACK GC_finalized_disclaim(void *obj)
 {
     word fc_word = *(word *)obj;
 
-    if ((fc_word & 1) != 0) {
+    if ((fc_word & FINALIZER_CLOSURE_FLAG) != 0) {
        /* The disclaim function may be passed fragments from the        */
        /* free-list, on which it should not run finalization.           */
        /* To recognize this case, we use the fact that the first word   */
@@ -34,7 +41,8 @@ STATIC int GC_CALLBACK GC_finalized_disclaim(void *obj)
        /* which does not use the first word for storing finalization    */
        /* info, GC_reclaim_with_finalization must be extended to clear  */
        /* fragments so that the assumption holds for the selected word. */
-        const struct GC_finalizer_closure *fc = (void *)(fc_word & ~(word)1);
+        const struct GC_finalizer_closure *fc
+                        = (void *)(fc_word & ~(word)FINALIZER_CLOSURE_FLAG);
         (*fc->proc)((word *)obj + 1, fc->cd);
     }
     return 0;
@@ -84,7 +92,7 @@ GC_API GC_ATTR_MALLOC void * GC_CALL GC_finalized_malloc(size_t lb,
     op = GC_malloc_kind(lb + sizeof(word), GC_finalized_kind);
     if (EXPECT(NULL == op, FALSE))
         return NULL;
-    *op = (word)fclos | 1;
+    *op = (word)fclos | FINALIZER_CLOSURE_FLAG;
     return op + 1;
 }