RFR: Implement flag to generate write-barriers without membars

[Aleksey Shipilev]

On 01/19/2018 06:43 PM, Roman Kennke wrote:
> Nothing should have changed since Roland's review.
> 
> http://cr.openjdk.java.net/~rkennke/wbwithmembar/webrev.01/
> 
> Ok to go?

OK for me.

-Aleksey