bug#25987: 25.2; support gcc fixit notes

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Thu, 9 Mar 2017 18:18:04 +0200
> 
> I'm not sure we want to tie this feature to compilation-mode. Many modes 
> that derive from it don't support fix-its, e.g. those of them that run 
> the test suites. And even for those that do, Compilation provides a very 
> basic UI.

So you suggest a separate minor mode, is that right?