preprocessor/10614: -Wtrigraphs does not catch // ??/

[Hallvard B Furuseth]

Neil Booth writes:
> You could persuade me that it's worthwhile warning for ??/ followed by
> a newline in any kind of comment with -Wtrigraphs.

Sounds good.  As I said in report preprocessor/10613, I think it's
important to warn about _silent_ changes from ISO C.

I suggest you also warn about ??/ <spaces/tabs> <newline>, since
gcc ignores these spaces/tabs (with a warning).

> it would warn about ??/ followed by a newline in C block comments that
> don't change behaviour, but I don't think that would bother those who
> want trigraph warnings off in comments.

Right.  If it bothers anyone, you could add a comment in the -Wtrigraphs
doc that ??/<newline> in comments is warned about because it _may_
change the meaning of the program, and leave it at that.

> Is that an acceptable compromise?

Yes, fine.

-- 
Hallvard