In order to avoid WARN/BUG from generating nested or even recursive
warnings, force rcu_is_watching() true during
WARN/lockdep_rcu_suspicious().

Notably things like unwinding the stack can trigger rcu_dereference()
warnings, which then triggers more unwinding which then triggers more
warnings etc..

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230126151323.408156109@infradead.org