Warnings about rcs_id strings: let's settle this

[Kean Johnston]

> For what it's worth, I agree that some variant of Kean's patch should
> be included.  I think some of the concerns raised in the discussion of
> the patch (enable at -Wextra? only for const variables?) should be
> addressed, but hopefully we can do that in short order without
> sidetracking again.

I too agree. I've read the whole thread, and had some other discussions
about the patch, and here's what I'm about to change it to do. I'd like
a nod from Joe, Gaby and you Zack, at the very least before I go
charging
off into vim-land again.

1) -Wall will NOT turn on -Wunused-static-variable
2) -Wextra WILL turn on -Wunused-static-variable
3) -Wunused-static-variable disappears out of c-opts.c and stays only
   in flags.h and toplev.c

And now, for the hard decision ... do I make the code check for const
variables only? I vote not, if for no other reason than the original
construct that spawned this thread was almost always written as
static char *sccsid = "blah";. By the way, why does THAT not emit a
warning? You are assigning a const char * to a char *, thereby
potentially losing the const-ness of it. I just tried with the head
version and -Wall -Wextra -Wcast-qual didn't emit a warning.

Kean