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_controller.c

@@ -1263,7 +1263,7 @@ nxt_controller_process_config(nxt_task_t *task, nxt_controller_request_t *req,
 
         /* Skip UTF-8 BOM. */
         if (nxt_buf_mem_used_size(mbuf) >= 3
-            && nxt_memcmp(mbuf->pos, "\xEF\xBB\xBF", 3) == 0)
+            && memcmp(mbuf->pos, "\xEF\xBB\xBF", 3) == 0)
         {
             mbuf->pos += 3;
         }
@@ -1940,7 +1940,7 @@ nxt_controller_process_control(nxt_task_t *task,
     }
 
     if (!nxt_str_start(path, "applications/", 13)
-        || nxt_memcmp(path->start + path->length - 8, "/restart", 8) != 0)
+        || memcmp(path->start + path->length - 8, "/restart", 8) != 0)
     {
         goto not_found;
     }