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>

sysdeps/unix/sysv/linux/dl-sysdep.c

@@ -113,7 +113,7 @@ _dl_sysdep_start (void **start_argptr,
   /* Initialize DSO sorting algorithm after tunables.  */
   _dl_sort_maps_init ();
 
-  __brk (0);			/* Initialize the break.  */
+  __brk (NULL);			/* Initialize the break.  */
 
 #ifdef DL_PLATFORM_INIT
   DL_PLATFORM_INIT;