hamt: Improve GCC 11 allocation-deallocation checking

[Bruno Haible]

2021-08-07  Bruno Haible  <bruno@clisp.org>

        hamt: Improve GCC 11 allocation-deallocation checking.
        * lib/hamt.h (hamt_free): Move declaration up.
        (hamt_create, hamt_copy): Declare that deallocation must happen through
        'hamt_free'.

diff --git a/lib/hamt.h b/lib/hamt.h
index 6bbc6a3..5d553fc 100644
--- a/lib/hamt.h
+++ b/lib/hamt.h
@@ -138,20 +138,22 @@ typedef void (Hamt_freer) (Hamt_entry *elt);
 /* Creation and Destruction */
 /****************************/
 
+/* Free the resources solely allocated by HAMT and all elements solely
+   contained in it.  */
+extern void hamt_free (Hamt *hamt);
+
 /* Create and return a new and empty hash array mapped trie.  */
 _GL_ATTRIBUTE_NODISCARD
 extern Hamt *hamt_create (Hamt_hasher *hasher, Hamt_comparator *comparator,
-                          Hamt_freer *freer);
+                          Hamt_freer *freer)
+  _GL_ATTRIBUTE_DEALLOC (hamt_free, 1);
 
 /* Return a copy of HAMT, which is not the same in the sense above.
    This procedure can be used, for example, so that two threads can
    access the same data independently.  */
 _GL_ATTRIBUTE_NODISCARD
-extern Hamt *hamt_copy (Hamt *hamt);
-
-/* Free the resources solely allocated by HAMT and all elements solely
-   contained in it.  */
-extern void hamt_free (Hamt *hamt);
+extern Hamt *hamt_copy (Hamt *hamt)
+  _GL_ATTRIBUTE_DEALLOC (hamt_free, 1);
 
 /**********/
 /* Lookup */