PATCH/RFC: Bring lin-lwp performance back to the real world

[Andrew Cagney]

> +#ifdef HAVE_PREAD64
> +  if (pread64 (fd, myaddr, len, addr) != len)
> +#else
> +  if (lseek (fd, addr, SEEK_SET) == -1
> +      || read (fd, myaddr, len) != len)
> +#endif

Suggest a comment explaining the rationale behind the choices and the 
need for those -D flags here.

Andrew