bug#25987: 25.2; support gcc fixit notes

[Tom Tromey <tom@tromey.com>]

>>>>> "Dmitry" == Dmitry Gutov <dgutov@yandex.ru> writes:

>> * One way for this to work would be to display the buffer and
>> show the proposed change as an overlay; and then use y-or-n-p
>> to ask whether it should be applied.  I was thinking something like:
[...]

Dmitry> I'm not sure we want to tie this feature to compilation-mode. Many
Dmitry> modes that derive from it don't support fix-its, e.g. those of them
Dmitry> that run the test suites. And even for those that do, Compilation
Dmitry> provides a very basic UI.

To me it seems very natural.  I compile, then as I next-error through
the results, Emacs offers to apply a change.

I think it's fine that some sub-modes don't support fix-its.  Actually I
don't understand how that would be a problem.  Presumably `grep' or
whatever isn't going to emit a fixit note anyhow.

Dmitry> Even to find and apply all fix-its, we'd need to add some new buffer,
Dmitry> to show the list.

That doesn't seem necessary to me either.

Tom