[PATCH] Document gdb.in/gdb.cmd files and debugredirect cli command

[Eli Zaretskii]

> From: Alan Hayward <Alan.Hayward@arm.com>
> CC: nd <nd@arm.com>, Alan Hayward <Alan.Hayward@arm.com>
> Date: Tue, 21 May 2019 09:08:01 +0000
> 
> Add missing documentation for the debugredirect setting.
> 
> Add description and uses of gdb.in/gdb.cmd to the testsuite README.
> 
> Mention this in the NEWS file.
> 
> [Wasn't sure if testsuite changes belonged in NEWS? If not I can
>  drop that part]
> ---
>  gdb/NEWS             | 11 +++++++++++
>  gdb/doc/gdb.texinfo  |  3 +++
>  gdb/testsuite/README | 21 +++++++++++++++++++++
>  3 files changed, 35 insertions(+)

This is OK, but please also update the 2 ChangeLog files.