bug#50840: 28.0.50; Support GNU style of multiline comments in C source code

[Juri Linkov]

> But there's no style to take a sequence of lines like this:
>
>      First line
>      continuation line with more text,
>      more text.  And another sentence
>      which continues here.
>
> and make it look like this:
>
>      /* First line
>         continuation line with more text,
>         more text.  And another sentence
>         which continues here.  */

Recently lisp/newcomment.el was fixed in bug#47167 and bug#50226
to handle whitespace in 'comment-continue' with the multi-line style.
So you can get the above with:

  (setq-local comment-style 'multi-line
              comment-continue "   ")

PS: It doesn't add double space at the sentence end
since this is a separate feature.