RFR: Back out: Avoid stub when calling to write-barrier from C2, remove all related code

[Aleksey Shipilev]

On 11/20/18 6:03 PM, Roman Kennke wrote:
> This patch breaks C1 and interpreter because they might also use xmm
> registers. At the very least, we need to put our register saving code
> back in. We need to consider what to do with C2.
> 
> I'll do the exact reverse of:
> http://cr.openjdk.java.net/~rkennke/remove-c2-wb-stub/webrev.02/
> 
> using "hg backout"

OK. Make sure synopsis mentions "backout".

-Aleksey