[PATCH, ld] Document purpose of each ld statement lists

[Nick Clifton]

Hi Thomas,

> *** ld/ChangeLog ***
> 
> 2018-11-28  Thomas Preud'homme  <thomas.preudhomme@linaro.org>
> 
>     * ldlang.c (statement_list): Document purpose and what next field it
>     uses.
>     (file_chain): Likewise.
>     (input_file_chain): Likewise.
>     * ldlang.h (lang_statement_header_type): Document statement list header
>     the next pointer correspond to.
>     (lang_statement_header_type): Replace comment for next and
>     next_real_file field to refer the reader to their corresponding
>     statement list header.

Approved - please apply.

Cheers
  Nick