[PATCH 2/5] Import idx.h from gnulib

[Florian Weimer]

* Adhemerval Zanella via Libc-alpha:

> diff --git a/include/idx.h b/include/idx.h
> new file mode 100644
> index 0000000000..ad7d31a2bc
> --- /dev/null
> +++ b/include/idx.h
> @@ -0,0 +1,113 @@
> +/* A type for indices and sizes.
> +
> +   Copyright (C) 2020 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 2, or (at your option)
> +   any later version.
> +
> +   This program is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> +   GNU General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program; if not, see <https://www.gnu.org/licenses/>.  */

This file is linked into the library itself, so we can only accept
something that is under a compatible license (probably LGPLv2 or later).