include: remove use of PTR

* hashtab.h (HTAB_EMPTY_ENTRY): Replace PTR with void *.
	(HTAB_DELETED_ENTRY): Likewise.

include/hashtab.h

@@ -79,12 +79,12 @@ typedef void (*htab_free_with_arg) (void *, void *);
 
 /* This macro defines reserved value for empty table entry.  */
 
-#define HTAB_EMPTY_ENTRY    ((PTR) 0)
+#define HTAB_EMPTY_ENTRY    ((void *) 0)
 
 /* This macro defines reserved value for table entry which contained
    a deleted element. */
 
-#define HTAB_DELETED_ENTRY  ((PTR) 1)
+#define HTAB_DELETED_ENTRY  ((void *) 1)
 
 /* Hash tables are of the following type.  The structure
    (implementation) of this type is not needed for using the hash