bug#8496: some file locking code in insert-file-contents cannot be right

[Paul Eggert]

As a result of the "mark unexported symbols 'static'" patch that I'm
working on, in the Emacs trunk I found some file-locking code inside
insert-file-contents that cannot be right:

     if (NILP (visit) && inserted > 0)
       {
   #ifdef CLASH_DETECTION
         if (!NILP (BVAR (current_buffer, file_truename))
             /* Make binding buffer-file-name to nil effective.  */
             && !NILP (BVAR (current_buffer, filename))
             && SAVE_MODIFF >= MODIFF)
           we_locked_file = 1;
   #endif /* CLASH_DETECTION */
         prepare_to_modify_buffer (GPT, GPT, NULL);
       }

The above code is equivalent to a no-op, since 'inserted' must
be zero here.  There's later code:

   #ifdef CLASH_DETECTION
         if (we_locked_file)
           unlock_file (BVAR (current_buffer, file_truename));
   #endif

that is also a no-op, because 'we_locked_file' must be zero.

GCC merrily optimizes all this code away, but I don't think
that was intended.  What *is* intended here?