Implement -Wimplicit-fallthrough (version 9)

[Tom Tromey]

>>>>> "Michael" == Michael Matz <matz@suse.de> writes:

Michael> All those bugs would also have been found as well when it had simply 
Michael> accepted
Michael>   /fall.*thr/i
Michael> anywhere in the preceding comment on one line.  But all the recent 
Michael> spelling changes of comments to cater for the strictness exactly shows how 
Michael> misguided that is.  The above would accept "Don't fall through" as well.  
Michael> I say: so what?

The point of the warning is to make code more robust.  But accepting any
comment like "Don't fall through" is not more robust, but rather an
error waiting to happen; as IIUC the user has no way to detect this
case.

I think it's better for the comment-scanning feature to be very picky
(or even just not exist at all) -- that way you know exactly what you
are getting.  Lint was traditionally picky IIRC.  And, this is a warning
that isn't default and can also be disabled, so it's not as if users
have no recourse.

Tom