bug#25987: 25.2; support gcc fixit notes

[Eli Zaretskii <eliz@gnu.org>]

> From: Tom Tromey <tom@tromey.com>
> Date: Sun, 05 Mar 2017 14:47:57 -0700
> 
> I think Emacs should support this in compilation mode buffers.

I agree, it would be a good feature.

> A few thoughts on the implementation:
> 
> * The filename quoting stuff will require a bit of unquoting

Perhaps shell-unquote-argument will help?

> * The offsets are byte offsets, not columns, which is a bit of a pain
>   (or at least, it is for me since I don't know how to handle that in
>   elisp)

Ouch! why did they do it in bytes?  That's worth a bug report, IMO.

Anyway, filepos-to-bufferpos could help with this problem.

> * One way for this to work would be to display the buffer and 
>   show the proposed change as an overlay;

Or maybe a tooltip on GUI frames?

> * However other approaches are possible, like letting the user request
>   no confirmation, or request "auto-apply all changes" or something.
>   Maybe a fixit should be associated with the previous error somehow.

Is there perhaps some "prior art" for this in other IDEs out there?

Thanks.