Silence most -Wzero-as-null-pointer-constant diagnostics

Replace 0 by NULL and {0} by {}.

Omit a few cases that aren't so trivial to fix.

Link: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117059>
Link: <https://software.codidact.com/posts/292718/292759#answer-292759>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

elf/dl-find_object.c

@@ -861,6 +861,6 @@ _dl_find_object_freeres (void)
           seg = previous;
         }
       /* Stop searching in shared objects.  */
-      _dlfo_loaded_mappings[idx] = 0;
+      _dlfo_loaded_mappings[idx] = NULL;
     }
 }