RFR (XS): Relax assert to not fire at safepoint

[Aleksey Shipilev]

On 03/07/2017 12:11 PM, Roman Kennke wrote:
> We're checking that a non-GC thread going into evacuate_object() does
> not hold the Threads_lock to prevent deadlock later.
> 
> However, it can happen that the VMThread gets there via
> biased-locking-revokation, and this guy does hold the Threads_lock when
> it does. It seems ok to me to get there in this case. It will end up
> waiting for evacuation to stop, which should also be ok, since we
> *don't* stop GC threads on non-GC pauses, and those will eventually turn
> off evacuation.
> 
> http://cr.openjdk.java.net/~rkennke/fixassert/webrev.01/

Sounds fine.

-Aleksey