[PATCH v2 1/4] linux: Move flockfile/_IO_flockfile into libc

[Florian Weimer]

* Adhemerval Zanella:

> The nptl version is used as default, since now with symbol always
> present the single-thread optimization is tricky.
>
> Hurd is not change, it is used it own lock scheme (which call
> _cthreads_flockfile).

Looks good to me.  Thanks.

If possible, please merge this today—I will start committing my stuff
tomorrow.

Florian