malloc: Sync dynarray with gnulib

It syncs with gnulib version a8bac4d49.  The main changes are:

  - Remove the usage of anonymous union within DYNARRAY_STRUCT.
  - Use DYNARRAY_FREE instead of DYNARRAY_NAME (free) so that
    Gnulib does not change 'free' to 'rpl_free'.
  - Use __nonnull instead of __attribute__ ((nonnull ())).
  - Use __attribute_maybe_unused__ instead of
    __attribute__ ((unused, nonnull (1))).
  - Use of _Noreturn instead of _attribute__ ((noreturn)).

The only difference with gnulib is:

--- glibc
+++ gnulib
@@ -18,6 +18,7 @@

 #include <dynarray.h>
 #include <stdio.h>
+#include <stdlib.h>

 void
 __libc_dynarray_at_failure (size_t size, size_t index)
@@ -27,7 +28,6 @@
   __snprintf (buf, sizeof (buf), "Fatal glibc error: "
               "array index %zu not less than array length %zu\n",
               index, size);
- __libc_fatal (buf);
 #else
  abort ();
 #endif

It seems a wrong sync from gnulib (the code is used on loader and
thus it requires __libc_fatal instead of abort).

Checked on x86_64-linux-gnu.

malloc/dynarray_resize_clear.c

@@ -17,7 +17,6 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <dynarray.h>
-#include <stdlib.h>
 #include <string.h>
 
 bool
@@ -28,7 +27,8 @@ __libc_dynarray_resize_clear (struct dynarray_header *list, size_t size,
   if (!__libc_dynarray_resize (list, size, scratch, element_size))
     return false;
   /* __libc_dynarray_resize already checked for overflow.  */
-  memset (list->array + (old_size * element_size), 0,
+  char *array = list->array;
+  memset (array + (old_size * element_size), 0,
           (size - old_size) * element_size);
   return true;
 }