Removed the unsafe nxt_memcmp() wrapper for memcmp(3).

The casts are unnecessary, since memcmp(3)'s arguments are 'void *'.
It might have been necessary in the times of K&R, where 'void *' didn't
exist.  Nowadays, it's unnecessary, and _very_ unsafe, since casts can
hide all classes of bugs by silencing most compiler warnings.

The changes from nxt_memcmp() to memcmp(3) were scripted:

$ find src/ -type f \
  | grep '\.[ch]$' \
  | xargs sed -i 's/nxt_memcmp/memcmp/'

Reviewed-by: Andrew Clayton <a.clayton@nginx.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>

src/nxt_application.c

@@ -366,7 +366,7 @@ nxt_discovery_module(nxt_task_t *task, nxt_mp_t *mp, nxt_array_t *modules,
                 &app->type, app->version, name);
 
         if (app->compat_length != sizeof(compat)
-            || nxt_memcmp(app->compat, compat, sizeof(compat)) != 0)
+            || memcmp(app->compat, compat, sizeof(compat)) != 0)
         {
             nxt_log(task, NXT_LOG_NOTICE, "incompatible module %s", name);