Mark CC_STACKPROTECTOR as being BROKEN

It's always been broken, but recent fixes actually made it do something,
and now the brokenness shows up as the resulting kernel simply not
working at all.

So it used to be that you could enable this config option, and it just
didn't do anything.  Now we'd better stop people from enabling it by
mistake, since it _does_ do something, but does it so badly as to be
unusable.

Code to actually make it work is pending, but incomplete and won't be
merged into 2.6.25 in any case.

Acked-by: Arjan van de Ven <arjan@infradead.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: James Morris <jmorris@namei.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>